bytesize instead of length

src/index.mjs

@@ -1,5 +1,6 @@
 import http from "http";
 import { URL } from "url";
+import { Buffer } from "buffer";
 import querystring from "querystring";
 
 import Router from "./router.mjs";
@@ -110,7 +111,7 @@ export default class flummpress {
     }) => {
       res.writeHead(code, {
         "content-type": `${type}; charset=UTF-8`,
-        "content-length": body.length
+        "content-length": Buffer.byteLength(body, 'utf-8')
       });
       if(res.method === 'HEAD')
         body = null;