Update to Apache 2.0 License.

package.json

@@ -16,7 +16,7 @@
     "url": "https://github.com/davideast/es6-shim.git"
   },
   "author": "",
-  "license": "MIT",
+  "license": "Apache 2.0",
   "bugs": {
     "url": "https://github.com/davideast/es6-shim/issues"
   },