Cleanup markdown sample code (#60)

* Use const/let in sample code

* run eslint on markdown code

* run eslint on markdown code

docs/prototype.serialize.md

@@ -9,10 +9,10 @@ Returns the serialized form of the simple-map, with any values in the map that
 have a serialize method also having serialized called.
 
 ```js
-var map = new SimpleMap();
-map.set("deep", new SimpleMap({a: "b"}));
+const map = new SimpleMap();
+map.set( "deep", new SimpleMap( { a: "b" } ) );
 
-map.serialize() //->  {deep: {a: "b"}}
+map.serialize(); //->  {deep: {a: "b"}}
 ```
 
 @return {Object} A plain JavaScript object that will only contain