Use const instead of let

Author: tshemsedinov

JavaScript/5-functor-ap.js

@@ -14,7 +14,7 @@ Maybe.prototype.ap = function(maybe) {
   ))));
 };
 
-let a = new Maybe(5);
-let f1 = new Maybe(x => x * 2);
-let f2 = new Maybe(x => ++x);
+const a = new Maybe(5);
+const f1 = new Maybe(x => x * 2);
+const f2 = new Maybe(x => ++x);
 a.ap(f1).ap(f2).map(console.log);