enable Array destructuring and polyfill Symbol class

app/assets/javascripts/commons/polyfills.js

@@ -4,6 +4,7 @@ import 'core-js/fn/object/assign';
 import 'core-js/fn/promise';
 import 'core-js/fn/string/code-point-at';
 import 'core-js/fn/string/from-code-point';
+import 'core-js/fn/symbol';
 
 // Browser polyfills
 import './polyfills/custom_event';

app/assets/javascripts/diff.js

@@ -34,10 +34,7 @@ class Diff {
   handleClickUnfold(e) {
     const $target = $(e.target);
     // current babel config relies on iterators implementation, so we cannot simply do:
-    // const [oldLineNumber, newLineNumber] = this.lineNumbers($target.parent());
-    const ref = this.lineNumbers($target.parent());
-    const oldLineNumber = ref[0];
-    const newLineNumber = ref[1];
+    const [oldLineNumber, newLineNumber] = this.lineNumbers($target.parent());
     const offset = newLineNumber - oldLineNumber;
     const bottom = $target.hasClass('js-unfold-bottom');
     let since;