Fix missing _ variable in param validator

lib/utils/parameter-validator.js

 var cJSON = require('circular-json')
+  , _ = require('lodash') // Don't require Utils here, as it creates a circular dependency
 
 var ParameterValidator = module.exports = {
   check: function(value, expectation, options) {
-    options = Utils._.extend({
+    options = _.extend({
       throwError:         true,
       deprecated:         false,
       deprecationWarning: generateDeprecationWarning(value, expectation, options),