remove Foreman from Gemfile

per @ddollar in https://github.com/ddollar/foreman/pull/437#issuecomment-41110407

> You should not put foreman into your Gemfile as the dependencies of a developer utility should not be able to interfere with the dependencies of your app.

later I told him I was using suspenders:

> Interesting I have always wondered where that trend got started. Having foreman be run inside the app using whatever random version of Ruby the user has installed is quite a pain point.