Add public method to Predicate class for customize validate message

[Rastopyr]

Hi guys,

this PR just add validateMessage method to Predicate class and should fix #122 , so it could be used in all cases of predicates:

// Chain from any predicate instance
ow.unicorn.validateMessage('We wait all unicorns')

// Chain from any predicate rule(because it the same predicate instance)
ow.unicorn.withRainbow.validateMessage('We wait all unicorns')

this method not affect any current features and not fail any test. It just extend predicate class.

P.S.:
I'm not sure that validateMessage is good name for this method, but message method already defined in some Predicate classes(error for example).

---

IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #122: Custom error message

---

IssueHunt has been backed by the following sponsors. Become a sponsor

[Rastopyr]

@sindresorhus linter is failing, but i'm pull it from last master. should i fix linter?

[Rastopyr]

But this PR still have a problem, predicates heritable from BasePredicate class not support this feature

[sindresorhus]

@Rastopyr Did you have a chance to look more into the problem?

[sindresorhus]

@Rastopyr Bump :)