Handle the FactoryGirl -> FactoryBot rename

[hrs]

The maintainers of FactoryGirl have decided to rename the project to FactoryBot. There's some logic in rspec-mode that uses the string "FactoryGirl", which may be an issue as folks switch over.

(Thanks so much for the great mode, by the way!)

[dgutov]

That's a bit non-trivial.

Should we rename the snippets as well? People who use them might have trouble adapting.

And we might have to parse the Gemfile, to see which factory gem is being used. Maybe we should just wait 6-12 months and rename it all then, leaving no compatibility with FactoryGirl.