use the sync function instead of the async function

tools/check-api.js

@@ -53,8 +53,7 @@ class API {
         console.log(error)
       })
     }
-
-    fs.writeFile(file, outLines.join('## '), () => {})
+    fs.writeFileSync(file, outLines.join('## '), () => {})
   }
 }