Fix warbler build, issue due rubygems changes

[JesseChavez]

This pull request fixes building warbler, issue reported in #522

JRuby 9.2.21.0

Downloading: mavengem:https://rubygems.org/org/jruby/jruby-complete/9.2.21.0/jruby-complete-9.2.21.0.jar
Downloading: https://repo.maven.apache.org/maven2/org/jruby/jruby-complete/9.2.21.0/jruby-complete-9.2.21.0.jar
Downloaded: https://repo.maven.apache.org/maven2/org/jruby/jruby-complete/9.2.21.0/jruby-complete-9.2.21.0.jar (28162 KB at 1876.0 KB/sec)
[INFO] ERROR:  While executing gem ... (OptionParser::InvalidOption)
[INFO]     invalid option: --no-rdoc
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 04:31 min
[INFO] Finished at: 2022-09-21T06:16:45+10:00
[INFO] Final Memory: 63M/260M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal de.saumya.mojo:gem-maven-plugin:1.1.5:initialize (default-initialize) on project warbler: Execution default-initialize of goal de.saumya.mojo:gem-maven-plugin:1.1.5:initialize failed: Java returned: 1 -> [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/PluginExecutionException

JRuby 9.3.8.0

Downloaded: https://repo.maven.apache.org/maven2/org/jruby/jruby-base/9.3.8.0/jruby-base-9.3.8.0.jar (8307 KB at 609.5 KB/sec)
Downloaded: https://repo.maven.apache.org/maven2/org/jruby/jruby-stdlib/9.3.8.0/jruby-stdlib-9.3.8.0.jar (13174 KB at 774.2 KB/sec)
[INFO] 
[INFO] --- gem-maven-plugin:1.1.5:initialize (default-initialize) @ warbler ---
Downloading: mavengem:https://rubygems.org/org/jruby/jruby-complete/9.3.8.0/jruby-complete-9.3.8.0.jar
Downloading: https://repo.maven.apache.org/maven2/org/jruby/jruby-complete/9.3.8.0/jruby-complete-9.3.8.0.jar
Downloaded: https://repo.maven.apache.org/maven2/org/jruby/jruby-complete/9.3.8.0/jruby-complete-9.3.8.0.jar (28739 KB at 2962.5 KB/sec)
[INFO] ERROR:  While executing gem ... (OptionParser::InvalidOption)
[INFO]     invalid option: --no-rdoc
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 45.787 s
[INFO] Finished at: 2022-09-21T06:31:43+10:00
[INFO] Final Memory: 57M/228M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal de.saumya.mojo:gem-maven-plugin:1.1.5:initialize (default-initialize) on project warbler: Execution default-initialize of goal de.saumya.mojo:gem-maven-plugin:1.1.5:initialize failed: Java returned: 1 -> [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/PluginExecutionException

The relevant fixes were applied to jruby-maven-plugins version 2.0.1

The failure is because rubygems removed --ri and --rdoc in version 3.0.1

More info at:
https://www.ruby-lang.org/en/news/2018/12/25/ruby-2-6-0-released/

[olleolleolle]

Good context in the description, thank you, and this looks like a fix we want. Awesome work!

CI: Jruby-head could perhaps (in some other PR) get replaced by/joined by a jruby 9.3.

[olleolleolle]

Ah, no, it's about rubygems installation. Unrelated to this change!

See also #512

[olleolleolle]

This looks good to me!