c7a0b9cee docs: use named import for javascript "direct import" fallback
Signed-off-by: Nicolas Coden <nicolas@ncoden.fr>
```js
// /!\ Don't use this if tree shaking works with standard named imports.
// Only Dropdown and DropdownMenu will be included in your application.
-import Dropdown from 'foundation-sites/js/foundation.dropdown';
-import DropdownMenu from 'foundation-sites/js/foundation.dropdownMenu';
+import { Dropdown } from 'foundation-sites/js/foundation.dropdown';
+import { DropdownMenu } from 'foundation-sites/js/foundation.dropdownMenu';
```
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