Update buildURL.js

Two if statements is unnecessary, we can replace with "if ... else ..."

lib/helpers/buildURL.js

@@ -41,9 +41,7 @@ module.exports = function buildURL(url, params, paramsSerializer) {
 
       if (utils.isArray(val)) {
         key = key + '[]';
-      }
-
-      if (!utils.isArray(val)) {
+      } else {
         val = [val];
       }