Fixed solution that was altered in git conflict

SunJieMing · SunJieMing · commit d525648a5970 · 2017-10-02T07:53:51.000-07:00
diff --git a/src/arrays.js b/src/arrays.js
@@ -22,7 +22,7 @@ const map = (elements, cb) => {
   return mappedArr;
 };
 
-const reduce = (elements, cb, startingValue) => {
+const reduce = (elements, cb, startingValue = elements.shift()) => {
   // Combine all elements into a single value going from left to right.
   // Elements will be passed one by one into `cb`.
   // `memo` is the starting value.  If `memo` is undefined then make `elements[0]` the initial value.
