feat: removes "isValid" from public API

BREAKING CHANGE: Gavel no longer exports "isValid" method from public API. Pleae use "gavel.validate" instead.

Author: artem-zakharchenko

lib/gavel.js

@@ -1,6 +1,5 @@
 const { HttpRequest, ExpectedHttpRequest } = require('./model/http-request');
 const { HttpResponse, ExpectedHttpResponse } = require('./model/http-response');
-const { isValid } = require('./validate');
 
 const validate = require('./next/validate');
 
@@ -12,6 +11,5 @@ module.exports = {
   HttpRequest,
   HttpResponse,
   ExpectedHttpRequest,
-  ExpectedHttpResponse,
-  isValid
+  ExpectedHttpResponse
 };