Bump to v4.1.0.

_WeakMap.js

@@ -0,0 +1,7 @@
+define(['./_getNative', './_root'], function(getNative, root) {
+
+  /* Built-in method references that are verified to be native. */
+  var WeakMap = getNative(root, 'WeakMap');
+
+  return WeakMap;
+});