fix: prevent memory leak

Author: D-Sketon

lib/plugins/filter/after_render/external_link.ts

@@ -44,7 +44,8 @@ function externalLinkFilter(this: Hexo, data: string): string {
   }
   result += data.slice(lastIndex);
 
-  return result;
+  // prevent gc memory leak
+  return result.replace('#'.repeat(result.length + 1), '');
 }
 
 export = externalLinkFilter;