Add support for RubyGems >= 2.0.0

RubyGems 2.0.0preview2 removed --no-rdoc and --no-ri options
for the install command.

(https://github.com/rubygems/rubygems/blob/master/History.txt)
21 jobs for master in 0 seconds
Status Job ID Name Coverage
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failed SlapOS.Eggs.UnitTest-Master.Python2

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