Use this, not $this

Used `this` instead of undefined `$this`, which currently sits out of scope where it is called.

Author: MasseyIsaako

javascript/ImageSelect.jquery.js

@@ -185,7 +185,7 @@
                     }
                 });
             });
-            $this.trigger('chosen:hiding_dropdown');
+            this.trigger('chosen:hiding_dropdown');
             return ret;
         }
     });