Merge pull request #70 from gitterHQ/revert-69-revert-68-optional_arr…

…ay_from_polyfill

Do not override "Array.from" with shim version if it is available.

See #68

src/lib/chat.js

@@ -1,5 +1,7 @@
 import {shim as arrayFromShim} from 'array.from';
-arrayFromShim();
+if (!Array.from) {
+  arrayFromShim();
+}
 import objectAssign from 'object-assign';
 import {Promise} from 'es6-promise';
 import Symbol from './basic-symbol-ponyfill';