@Fryguy Looks good to me. I do have one nit/comment/question.

http://guides.rubygems.org/specification-reference/
defines both add_development_dependency and add_runtime_dependency
but does not mention the add_dependency alias for add_runtime_dependency.
For me being a new-ish-bie to ruby it took me a bit longer to find the meaning
of add_dependency and I initial assumed that you perhaps made a typo.

Is the alias add_dependency widely used?

Why not avoid the alias and use the well documented add_runtime_dependency
instead?