Amend regex to prevent incorrect boolean return type

[ImClarky]

Currently, any method name beginning with can, is or has is assumed to return type boolean. However this is not always the case, as method names like cancel or hash will not necessarily return a boolean.

This PR updates the regex to look for an uppercase letter, or an underscore (for CodeIgniter for example), directly after can, is or has to assert that will probably return boolean.

The change also adds should as an boolean-y prefix.

I changed the regex to /^(is|has|can|should)[A-Z_]/ but this would not apply for methods literally called can, is, has or should. Could update to /^(is|has|can|should)(?:[A-Z_]|$)/

[neild3r]

@ImClarky can you merge in master to get the builds going again and add some test cases for the the problem you encountered. I feel like we could also account for digits here as well