fix incorrect reference. fixes #1530

select2.js

@@ -2978,7 +2978,7 @@ the specific language governing permissions and limitations under the Apache Lic
                     self.updateSelection(data);
                     self.clearSearch();
                     if (triggerChange) {
-                        self.triggerChange(this.buildChangeDetails(oldData, this.data()));
+                        self.triggerChange(self.buildChangeDetails(oldData, this.data()));
                     }
                 });
             }