Change assert function for correct test cases

[diegonvs]

I'm reviewing the tests on validators and i’ve saw a problem that the usage of assert.ok() is probably not adequate in our tests, maybe we can use assert.isTrue().

Taking this hypothesis:

	it('should validate any type', function() {
		const validator = validators.any();
		assert.ok(validator('testString'));
		assert.ok(validator(false));
		assert.ok(validator({}));
		assert.ok(validator(1));
		assert.ok(validator(function() {}));
		assert.ok(new Error(“something”));
	});

If validators.any() function is broken, these tests will pass no matter what that function returns (unless it returns false - which we never return). I suggest we change from assert.ok to assert.isTrue to verify cases that passes/corrects.

[diegonvs]

pr: #278

[robframpton]

#278 merged, thanks!