Added strict mode to Class

Author: montogeek

lib/MemoryFileSystem.js

@@ -2,6 +2,7 @@
 	MIT License http://www.opensource.org/licenses/mit-license.php
 	Author Tobias Koppers @sokra
 */
+"use strict";
 
 const normalize = require("./normalize");
 const join = require("./join");