Fix handling of missing common.js jQuery dependency.

Author: paulmillr

lib/header.js

@@ -1,5 +1,5 @@
 /*!
- * Exoskeleton.js 0.6.0
+ * Exoskeleton.js 0.6.1
  * (c) 2013 Paul Miller <http://paulmillr.com>
  * Based on Backbone.js
  * (c) 2010-2013 Jeremy Ashkenas, DocumentCloud
@@ -14,9 +14,9 @@
       root.Backbone = root.Exoskeleton = factory(root, exports, _, $);
     });
   } else if (typeof exports !== 'undefined') {
-    var _, jquery;
+    var _, $;
     try { _ = require('underscore'); } catch(e) { }
-    try { jquery = require('jquery'); } catch(e) { }
+    try { $ = require('jquery'); } catch(e) { }
     factory(root, exports, _, $);
   } else {
     root.Backbone = root.Exoskeleton = factory(root, {}, root._, (root.jQuery || root.Zepto || root.ender || root.$));