Brew still using 1.8 ruby verison. but OSX 10.10 ship with 2.0.0 so symoblinking for now.
$ sudo mkdir -p /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin
$ sudo ln -s /usr/bin/ruby /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby