Loosen pundit restrictions…

As far as I can tell, `pundit 0.3` (current version) will still work with `pundit_helpers`.
@halostatue thanks for pointing this out!

I think this will only allow for >= 0.2.1 and < 0.3 so it won't  support pundit 0.3 with this change.  I may be misunderstanding versioning though.

Maybe `>= 0.2.1` would do the trick for now?