Typo in addAction function: _.findIdnex should be .findIndex, fixes unresolved function

Author: ikk0

app/code/Magento/Ui/view/base/web/js/grid/massactions.js

@@ -98,7 +98,7 @@ define([
          */
         addAction: function (action) {
             var actions = this.actions(),
-                index = _.findIdnex(actions, {
+                index = _.findIndex(actions, {
                     type: action.type
                 });