Error occur when execute mvn Test site command

When I execute "mvn test site", encounter following error(see below).
pom.xml file is attached for your reference.

Please help and advise

Thanks.

-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running TestSuite
Configuring TestNG with: org.apache.maven.surefire.testng.conf.TestNG652Configurator@ba8a1dc
*********App Test Maven***********
*********sample Test***********
Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.39 sec

Results :

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0

[INFO]
[INFO] --- maven-site-plugin:3.3:site (default-site) @ learntestng ---
[INFO] configuring report plugin org.reportyng:reporty-ng:1.2
[WARNING] The POM for org.reportyng:reporty-ng:jar:1.2 is missing, no dependency information available
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.951 s
[INFO] Finished at: 2017-02-06T12:07:52-05:00
[INFO] Final Memory: 20M/353M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-site-plugin:3.3:site (default-site) on project learntestng: failed to get report for org.reportyng:reporty-ng: Plugin org.reportyng:reporty-ng:1.2 or one of its dependencies could not be resolved: Failure to find org.reportyng:reporty-ng:jar:1.2 in https://github.com/apache/maven was cached in the local repository, resolution will not be reattempted until the update interval of reporty-ng has elapsed or updates are forced -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException