Update ffaker gem

Adds a version requirement which it didn't have before, at 2.0.0. This version has breaking API changes in that the namespace is now `FFaker` instead of `Faker`.

Prior, if a new developer checked out the repo, ran `bundle install` and then tried `rake dev:setup`, seeding would fail due to having the latest version of ffaker without the API changes in this MR.

Also updates `spring` version and the binstubs, just for kicks.

See merge request !686