Add rule disallowing toBeTruthy

[marekdedic]

Hi,
there is a rule preferring toBeTruthy over toBe(true). However, the truthy matcher does type coercion, which may be unwanted. I'd appreciate a reverse rule which triggers on .toBeTruthy and enforces the use of matchers without type coercion (like .toBe(true)).

dtto for toBeFalsy.

I'm willing to make a PR if I get a go-ahead from the maintainers.