Fix typo

Author: benoitvallon

data-structures-in-javascript/set.es6.js

@@ -20,7 +20,7 @@ class Set {
   }
 
   contains(value) {
-    return this.values.indexOf(value) !==  -1;
+    return this.values.indexOf(value) !== -1;
   }
 
   union(set) {

data-structures-in-javascript/set.js

@@ -17,7 +17,7 @@ Set.prototype.remove = function(value) {
   }
 };
 Set.prototype.contains = function(value) {
-  return this.values.indexOf(value) !==  -1;
+  return this.values.indexOf(value) !== -1;
 };
 Set.prototype.union = function(set) {
   var newSet = new Set();