[rails4] upgrade to ruby 2.0.0-p247

Update the Ruby version [as dicussed](https://groups.google.com/forum/#!topic/rubygems-org/2FEuTDa3NnI). 

cc\ @geemus @sferik -  given your involvement in https://github.com/fog/fog/pull/1890 nokogiri 1.6.0 bump, any insights on why fog/nokogiri are tangled in the build error?