Add Library Dependency for installing mysql2 gem

When deploying [Supermarket app](https://github.com/opscode/supermarket), chef cookbook
fails provisioning due to mysql2 gem not being able to be installed. Mysql2 gem depends on
libmysqlclient-dev and also on libmysql-ruby.

[This StackOverflow](http://stackoverflow.com/questions/3608287/error-installing-mysql2-failed-to-build-gem-native-extension) post shows the dependency.

Signed-off-by: "Jake Champlin" <jake.champlin.27@gmail.com>