build: update url_launcher

lib/models/auth.dart

@@ -742,7 +742,7 @@ class AuthModel with ChangeNotifier {
     final repoScope = publicOnly ? 'public_repo' : 'repo';
     final scope = Uri.encodeComponent(
         ['user', repoScope, 'read:org', 'notifications'].join(','));
-    launchUrl(
+    launchStringUrl(
       'https://github.com/login/oauth/authorize?client_id=$clientId&redirect_uri=gittouch://login&scope=$scope&state=$_oauthState',
     );
   }

lib/models/theme.dart

@@ -259,7 +259,7 @@ class ThemeModel with ChangeNotifier {
         replace: replace,
       );
     } else {
-      launchUrl(url);
+      launchStringUrl(url);
     }
   }