Fix issue where popperjs spammed console warnings

```
`preventOverflow` modifier is required by `hide` modifier in order to work, be sure to include it before `hide`!
```

- Needed `hide` - https://popper.js.org/docs/v2/modifiers/hide/

shell/components/nav/TopLevelMenu.vue

@@ -242,7 +242,7 @@ export default {
         return {
           content:       this.shown ? null : item,
           placement:     'right',
-          popperOptions: { modifiers: { preventOverflow: { enabled: false } } }
+          popperOptions: { modifiers: { preventOverflow: { enabled: false }, hide: { enabled: false } } }
         };
       } else {
         return { content: undefined };