Add ruby lib to folders handled specially by keg.link

Library/Homebrew/keg.rb

@@ -62,6 +62,7 @@ class Keg <Pathname
       when /^perl5/ then :mkpath
       when 'php' then :mkpath
       when /^python[23]\.\d$/ then :mkpath
+      when 'ruby' then :mkpath
       # Everything else is symlinked to the cellar
       else :link
       end