gem-maven-plugin uses the deprecated "--no-rdoc" command

[Riduidel]

When running the initialize command, I get the following error message

[WARNING] ERROR:  While executing gem ... (OptionParser::InvalidOption)
    invalid option: --no-rdoc```

According to https://github.com/rubygems/heroku-buildpack-bundler2/pull/1#issuecomment-451654992, it seems like the `--no-rdoc` flag is deprecated and should be replaced by `--no-document`.

[Riduidel]

Seems to have been introduced in "recent" JRuby version ... (build fails with JRuby>=9.2.10.0)

[deivid-rodriguez]

This was fixed by https://github.com/torquebox/jruby-maven-plugins/pull/106, but it's not yet released.

[deivid-rodriguez]

It has been released now as gem-maven-plugin 2.0.0. However, I think we accidentally drop support for Java 8, so depending on the Java you're using, it might not do the trick for you. I expect to fix that on #119.

[deivid-rodriguez]

This can be closed in any case.