Update array iteration on checkCredential method

lib/client.js

@@ -53,7 +53,7 @@ var basicRequest = function (url, apiKey, method, body, callback) {
  * @returns {boolean}
  */
 var checkCredential = function (credentialName, credential) {
-  for (var i = 0, credentialLen = ALLOWED_CREDENTIALS.length; i < credentialLen; i++) {
+  for (var i = 0; i < ALLOWED_CREDENTIALS.length; i++) {
     if (ALLOWED_CREDENTIALS[i].name === credentialName) {
       if (typeof credential !== ALLOWED_CREDENTIALS[i].type) {
         throw credentialName + ' must be a ' + ALLOWED_CREDENTIALS[i].type;