Update 3.insertionSort.md

Author: Rain120

3.insertionSort.md

@@ -21,16 +21,14 @@
 
 ```js
 function insertionSort(arr) {
-    var len = arr.length;
-    var preIndex, current;
-    for (var i = 1; i < len; i++) {
+    var preIndex;
+    for (var i = 1; i < arr.length; i++) {
         preIndex = i - 1;
-        current = arr[i];
-        while(preIndex >= 0 && arr[preIndex] > current) {
-            arr[preIndex+1] = arr[preIndex];
+        while(preIndex >= 0 && arr[preIndex] > arr[i]) {
+            arr[preIndex + 1] = arr[preIndex];
             preIndex--;
         }
-        arr[preIndex+1] = current;
+        arr[preIndex + 1] = arr[i];
     }
     return arr;
 }