Use a postscript font names to fix issues in OSX 10.9.
Cherry picked from:
https://github.com/paulwittmann/rails-erd/commit/5cd4e5d4b86520eae5f9d8845ffb214ee92e9d92
https://github.com/paulwittmann/rails-erd/commit/9ccb094fa29b095d5549271f48c65af8bb53f749