cleanup: Disambiguate assignments in arrow functions

As arrow functions have an implicit return value, an assignment of
this.foo = bar could have been intended as a this.foo === bar
comparison. To catch those errors, we will disallow these kinds
of assignments unless they are marked explicitly by an extra pair
of parentheses.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/731

js/ui/workspacesView.js

@@ -247,7 +247,7 @@ var WorkspacesView = class extends WorkspacesViewBase {
         this.scrollAdjustment.ease(index, {
             mode: Clutter.AnimationMode.EASE_OUT_QUAD,
             duration: WORKSPACE_SWITCH_TIME,
-            onComplete: () => this._animatingScroll = false
+            onComplete: () => (this._animatingScroll = false)
         });
     }