Added typeof check to Symbol in isIterable to avoid throwing a

ReferenceError in iOS 8.0, mobile Safari 600.1.4

Author: Darren Thompson

src/isIterable.js

@@ -1,6 +1,6 @@
 import _ from 'lodash';
 
-const ITERATOR_SYMBOL = _.isFunction(Symbol) && Symbol.iterator;
+const ITERATOR_SYMBOL = typeof Symbol !== 'undefined' && _.isFunction(Symbol) && Symbol.iterator;
 const OLD_ITERATOR_SYMBOL = '@@iterator';
 
 /**