Add trailing slash warning

lib/ui/app/dialogs/health_check_dialog.dart

@@ -167,6 +167,12 @@ class _HealthCheckDialogState extends State<HealthCheckDialog> {
                     isWarning: true,
                     url:
                         'https://invoiceninja.github.io/docs/self-host-troubleshooting/#pdf-conversion-issues',
+                  ),
+                if (_response.trailingSlash)
+                  _HealthListTile(
+                    title: 'APP_URL has trailing slash',
+                    subtitle: 'Remove the slash in the .env file',
+                    isWarning: true,
                   )
               ],
             ),

lib/ui/app/menu_drawer.dart

@@ -1263,16 +1263,16 @@ void _showAbout(BuildContext context) async {
                   Row(
                     mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                     children: [
-                      IconButton(
-                        tooltip: 'Facebook',
-                        onPressed: () => launch(kFacebookUrl),
-                        icon: Icon(MdiIcons.facebook),
-                      ),
                       IconButton(
                         tooltip: 'Twitter',
                         onPressed: () => launch(kTwitterUrl),
                         icon: Icon(MdiIcons.twitter),
                       ),
+                      IconButton(
+                        tooltip: 'Facebook',
+                        onPressed: () => launch(kFacebookUrl),
+                        icon: Icon(MdiIcons.facebook),
+                      ),
                       IconButton(
                         tooltip: 'GitHub',
                         onPressed: () => launch(kGitHubUrl),