Changed let to var for consistency

Author: struct78

lib/array.js

@@ -444,9 +444,9 @@ helpers.map = function(array, iter) {
 
 helpers.pluck = function(arr, prop) {
   if (util.isUndefined(arr)) return '';
-  let res = [];
-  for (let i = 0; i < arr.length; i++) {
-    let val = utils.get(arr[i], prop);
+  var res = [];
+  for (var i = 0; i < arr.length; i++) {
+    var val = utils.get(arr[i], prop);
     if (typeof val !== 'undefined') {
       res.push(val);
     }