Update ajax_variable_list.js to use lodash escape

app/assets/javascripts/ci_variable_list/ajax_variable_list.js

-import _ from 'underscore';
+import { escape as esc } from 'lodash';
 import axios from '../lib/utils/axios_utils';
 import { s__ } from '../locale';
 import Flash from '../flash';
@@ -10,7 +10,7 @@ function generateErrorBoxContent(errors) {
   const errorList = [].concat(errors).map(
     errorString => `
     <li>
-      ${_.escape(errorString)}
+      ${esc(errorString)}
     </li>
   `,
   );