chore: add update_url only for self-served Firefox version

gulpfile.js

@@ -77,7 +77,7 @@ gulp.task('manifest', () => (
     data.version = pkg.version.replace(/-[^.]*/, '');
     if (process.env.TARGET === 'firefox') {
       data.version += 'f';
-      delete data.applications.gecko.update_url;
+      data.applications.gecko.update_url = 'https://violentmonkey.top/static/updates.json';
     }
     file.path = file.path.replace(/\.yml$/, '.json');
     return JSON.stringify(data);

src/manifest.yml

@@ -43,4 +43,3 @@ permissions:
 applications:
   gecko:
     id: '{aecec67f-0d10-4fa7-b7c7-609a2db280cf}'
-    update_url: https://violentmonkey.top/static/updates.json