Implement a server for testing

[azu]

Some tests have been disabled in #156.

https://httpstat.us/ was out of service, so I think we should have a test server using Node.js in this repository instead.
textlint-tester can use mocha, so you should be able to set up a test like this

// http//localhost4323
describe("no-dead-link", () =>{
  let closeServer;
  before(() => {
    closeServer = await startServer(); // "/200", "/500" etc...
  });
  after(() => { 
    closeServer();
  })
  textlintTester.run(...
})