Update keyboard.js

lol you are right i didn't follow the whole conversation because I couldn't understand why it mattered since an array is an object also... but why don't we make it an empty object without the Object.prototype. By using Object.create(null);

Author: darbicus

src/input/keyboard.js

@@ -230,7 +230,7 @@ define(function (require) {
    * been released.
    */
   p5.prototype.onblur = function (e) {
-    downKeys =[];
+    downKeys ={};
   };
 
   /**