Add not_in to list of validation rules
It should be notin instead of not_in

Signed-off-by: Dries Vints <dries.vints@gmail.com>
I'm an idiot. It should be not_in

Silly me :-/ sorry for the duplicate commit.

Signed-off-by: Dries Vints <dries.vints@gmail.com>
Merge pull request #163 from driesvints/patch-2

Add not_in to list of validation rules