add select2 destroy method

src/inputs/select2/select2.js

@@ -229,6 +229,12 @@ $(function(){
                 }
             }
             return source;            
+        },
+        
+        destroy: function() {
+            if(this.$input.data('select2')) {
+                this.$input.select2('destroy');
+            }
         }               
         
     });