Update RI files for Ruby 2.1.5

[tknerr]

RubyInstaller with Ruby 2.1.5 had been released a few weeks ago:
http://rubyinstaller.org/news/2014/11/18/rubyinstaller-1-9-3-p551-2-0-0-p598-and-2-1-5-released/

Do the RI files need an update for that?

/cc @luislavena

[tknerr]

Indeed the RI files for Ruby 2.1.0 are missing:

D:\Repos\_github\ruby-devpack\target\build>ruby -v
ruby 2.1.5p273 (2014-11-13 revision 48405) [x64-mingw32]

D:\Repos\_github\ruby-devpack\target\build>rdoc-data --install
Your ruby version 2.1.5 is not supported, only 1.8.7, 1.9.2, 1.9.3, 2.0.0

[zzak]

@drbrain Do you remember how to generate the data for rdoc?

[zzak]

This should be fixed by upgrading to version 4.1.0.

Thanks for your patience!