Add repeatStr function implementation

Implemented repeatStr function without using String.prototype.repeat.

Author: cywong-dev

Sprint-3/2-practice-tdd/repeat-str.js

@@ -1,7 +1,8 @@
 function repeatStr() {
   // Your implementation of this function must *not* call String.prototype.repeat (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/repeat).
   // The goal is to re-implement that function, not to use it.
-
+    let result = "";
+  
     for (let i = 0; i < count; i++) {
         result += str;
     }