* lib/rubygems/specification.rb:  Include 2.2.0.preview.2 when checking
  if extensions should be built.  Fixes a ruby-ci failure.
* test/rubygems/test_gem_specification.rb:  Test for the above.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43646 b2dd03c8-39d4-4d8f-98ff-823fe69b080e