Loosen pundit restrictions…

As far as I can tell, `pundit 0.3` (current version) will still work with `pundit_helpers`.
No; `~> 0.2.1` acts like `>= 0.2.1, < 0.3`. `~> 0.2` acts like `>= 0.2, < 1.0`.

You want to avoid `>=` comparisons as much as possible, unless you’re going to make it something like `>= 0.2.1, < 1.0`.