refactor;: use const for static value

Author: azu

Diff for: src/connect/connect-echo-example.js

@@ -20,7 +20,7 @@ let server = http.createServer(app).listen(3000, request);
 // request => response
 function request() {
     let closeServer = server.close.bind(server);
-    let requestBody = {
+    const requestBody = {
         "key": "value"
     };
     fetch("http://localhost:3000", {

Diff for: test/connect/hello-test.js

@@ -9,7 +9,7 @@ import echo from "../../src/connect/echo";
 import http from "http";
 import fetch from "node-fetch";
 describe("connect", function () {
-    let responseText = "test";
+    const responseText = "test";
     let server;
     describe("errorHandler", function () {
         beforeEach(function (done) {