refactor;: use const for static value

Author: azu

Diff for: src/ESLint/MyLinter-example.js

@@ -5,7 +5,7 @@ import noConsole from "./no-console";
 
 let linter = new MyLinter();
 linter.loadRule(noConsole);
-let code = `
+const code = `
 function add(x, y){
     console.log(x, y);
     return x + y;

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

@@ -77,9 +77,9 @@ describe("connect", function () {
             server && server.close();
         });
         it("should return request as response", function () {
-            let requestBody = {
+            const requestBody = Object.freeze({
                 key: "value"
-            };
+            });
             return fetch("http://localhost:3000", {
                 method: "POST",
                 headers: {