Update select2.js

Fix for when you specify tags using JSON-encoded select2-tags-attribute.

And thank you for properly implementing my (earlier) submitted hack :)

select2.js

@@ -794,7 +794,7 @@ the specific language governing permissions and limitations under the Apache Lic
                 if ("tags" in opts) {
                     throw "tags specified as both an attribute 'data-select2-tags' and in options of Select2 " + opts.element.attr("id");
                 }
-                opts.tags=opts.element.attr("data-select2-tags");
+                opts.tags=opts.element.data("select2Tags");
             }
 
             if (select) {