Hide the mobile menu when a menu item gets clicked

In the common case of the user just targeting an activity and not
browsing the menu the user wants the menu to be gone right away.

packages/app-shell/src/app-shell.js

@@ -306,6 +306,7 @@ export class AppShell extends ScopedElementsMixin(LitElement) {
         const link = e.composedPath()[0];
         const location = link.getAttribute('href');
         this.router.updateFromPathname(location);
+        this.toggleMenu();
     }
 
     onLanguageChanged(e) {