therubyracer install error

@Haegin's answer in https://github.com/cowboyd/libv8/issues/205

brew uninstall v8
brew install v8-315
gem uninstall -a libv8
gem uninstall -a therubyracer
gem install libv8 -v '3.16.14.17' -- --with-system-v8
gem install therubyracer -v '0.12.2' -- --with-v8-dir=$(brew --prefix v8-315)

You can use the Libv8 from the brew instead of the one from gem. You can do that by following commands:

$ gem uninstall libv8
$ brew install v8
$ gem install therubyracer