Unable to set up, files don't download due to the following error "unable to find valid certification path to requested target"

While trying to set up sikuliX v. 1.1.1, the setup seems to fail and I'm unable to aquire the .cmd file. The setup log looks like the following: (my username replaced with my_username)

[debug (07.09.17 08:30:52)] Debug: setLogFile: U:\SikuliX\SikuliX-1.1.1-SetupLog.txt
[debug (07.09.17 08:30:52)] RunSetup: ... starting with no args given
[debug (07.09.17 08:30:52)] RunSetup: Setup: 1.1.1 2017-03-29_10:41 in folder:
U:\SikuliX
[debug (07.09.17 08:30:53)] RunSetup: RunningSystem: Windows 6.1
[debug (07.09.17 08:30:53)] RunSetup: parent of jar/classes: U:\SikuliX
[debug (07.09.17 08:30:53)] RunSetup: RunningJava: Java 8 (amd64) 1.8.0_131-b11
[debug (07.09.17 08:30:53)] init user preferences
[debug (07.09.17 08:30:57)] RunSetup:
popAsk: --------------------
The following file(s) will be downloaded to
U:\SikuliX
--- Native support libraries for Windows (sikulixlibs...)
--- Package 1 ---
null (IDE/Scripting)
null (Java API)
 - with Jython
Only click NO, if you want to terminate setup now!
Click YES even if you want to use local copies in Downloads!
--------------------
[debug (07.09.17 08:31:02)] FileManager: download to string from:
https://oss.sonatype.org/content/groups/public/com/sikulix/sikulixlibswin/1.1.1-SNAPSHOT/maven-metadata.xml,
[error (07.09.17 08:31:02)] FileManager: problems while downloading
sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[error (07.09.17 08:31:02)] RunSetup: Maven download: could not get timestamp nor buildnumber for sikulixlibswin from:
https://oss.sonatype.org/content/groups/public/com/sikulix/sikulixlibswin/1.1.1-SNAPSHOT/maven-metadata.xml
with content:

[debug (07.09.17 08:31:02)] RunSetup:
popAsk: --------------------
You have for Java API package
D:\Users\my_username\AppData\Roaming\Sikulix\SikulixDownloads_201703291041\sikulixsetupAPI-1.1.0-forsetup.jar
Click YES, if you want to use this for setup processing
... or click NO, to ignore it and download a fresh copy
--------------------
[debug (07.09.17 08:31:19)] FileManager: download to string from:
https://oss.sonatype.org/content/groups/public/com/sikulix/sikulixsetupAPI/1.1.1-SNAPSHOT/maven-metadata.xml,
[error (07.09.17 08:31:20)] FileManager: problems while downloading
sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[error (07.09.17 08:31:20)] RunSetup: Maven download: could not get timestamp nor buildnumber for sikulixsetupAPI#forsetup from:
https://oss.sonatype.org/content/groups/public/com/sikulix/sikulixsetupAPI/1.1.1-SNAPSHOT/maven-metadata.xml
with content:

[debug (07.09.17 08:31:20)] RunSetup:
popAsk: --------------------
You have for SikuliX IDE package
D:\Users\my_username\AppData\Roaming\Sikulix\SikulixDownloads_201703291041\sikulixsetupIDE-1.1.0-forsetup.jar
Click YES, if you want to use this for setup processing
... or click NO, to ignore it and download a fresh copy
--------------------
[debug (07.09.17 08:31:21)] FileManager: download to string from:
https://oss.sonatype.org/content/groups/public/com/sikulix/sikulixsetupIDE/1.1.1-SNAPSHOT/maven-metadata.xml,
[error (07.09.17 08:31:21)] FileManager: problems while downloading
sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[error (07.09.17 08:31:21)] RunSetup: Maven download: could not get timestamp nor buildnumber for sikulixsetupIDE#forsetup from:
https://oss.sonatype.org/content/groups/public/com/sikulix/sikulixsetupIDE/1.1.1-SNAPSHOT/maven-metadata.xml
with content:

[debug (07.09.17 08:31:21)] RunSetup:
popAsk: --------------------
If you click YES, you will get Jython version 2.7.0 (recommended)
... but in rare cases there might be issues with UTF-8/Unicode
that usually appear on startup when UTF-8 characters
are present somewhere in the system environment
If you encounter such problems with Jython 2.7.0
run setup again and
click NO to get Jython 2.5.4rc1
--------------------
[debug (07.09.17 08:31:25)] RunSetup:
popAsk: --------------------
You have for Jython 2.7
D:\Users\my_username\AppData\Roaming\Sikulix\SikulixDownloads\jython-standalone-2.7.0.jar
Click YES, if you want to use this for setup processing
... or click NO, to ignore it and download a fresh copy
--------------------
[debug (07.09.17 08:31:28)] FileManager: Downloading jython-standalone-2.7.0.jar having 36154 KB
[debug (07.09.17 08:31:52)] FileManager: downloaded 36154 KB to:
D:\Users\my_username\AppData\Roaming\Sikulix\SikulixDownloads\jython-standalone-2.7.0.jar
[debug (07.09.17 08:31:52)] FileManager: download time: 24
[debug (07.09.17 08:33:28)] RunSetup: Copied from Downloads: Jython
[debug (07.09.17 08:33:28)] RunSetup: Download ended
[debug (07.09.17 08:33:28)] RunSetup: Downloads for selected options:
null null null jython-standalone-2.7.0.jar
[debug (07.09.17 08:33:28)] RunSetup:
popError: --------------------
Some of the downloads did not complete successfully.
Check the logfile for possible error causes.
If you think, setup's inline download is blocked somehow on
your system, you might download the appropriate raw packages manually
into the folder Downloads in the setup folder and run setup again.
files to download (information is in the setup log file too)
null
null
null
jython-standalone-2.7.0.jar
Be aware: The raw packages are not useable without being processed by setup!
For other reasons, you might simply try to run setup again.
--------------------
[error (07.09.17 08:33:36)] RunSetup: download not completed successfully
[error (07.09.17 08:33:36)] RunSetup: ... terminated abnormally :-(
[debug (07.09.17 08:33:36)] RunSetup:
popError: --------------------
Something serious happened! Sikuli not useable!
Check the error log at U:\SikuliX\SikuliX-1.1.1-SetupLog.txt
--------------------
[debug (07.09.17 08:33:37)] RunTimeSETUP: final cleanup
[debug (07.09.17 08:33:38)] FileManager: deleteFileOrFolder:
D:\Users\my_username\AppData\Local\Temp\Sikulix_1412793441