Fixed travis

- Tests against Node 4, 8, 10, 12 and newest

Modernized:
- Use arrow functions
- Use string templates in examples and some code
- Use single quote for strings

test/authorizer_namespaces.test.js

@@ -2,46 +2,43 @@ const fixture = require('./fixture/namespace');
 const request = require('request');
 const io = require('socket.io-client');
 
-describe('authorizer with namespaces', function () {
+describe('authorizer with namespaces', () => {
 
   //start and stop the server
   before(fixture.start);
-
   after(fixture.stop);
 
-  describe('when the user is not logged in', function () {
+  describe('when the user is not logged in', () => {
 
-    it('should be able to connect to the default namespace', function (done) {
+    it('should be able to connect to the default namespace', (done) => {
       io.connect('http://localhost:9000')
-        .once('hi', done);
+        .once('hi', () => done());
     });
 
-    it('should not be able to connect to the admin namespace', function (done) {
+    it('should not be able to connect to the admin namespace', (done) => {
       io.connect('http://localhost:9000/admin')
-        .once('disconnect', function() { done(); })
-        .once('hi admin', function() {
-          done(new Error('unauthenticated client was able to connect to the admin namespace'));
-        });
+        .once('disconnect', () => done())
+        .once('hi admin', () => done(new Error('unauthenticated client was able to connect to the admin namespace')));
     });
 
   });
 
-  describe('when the user is logged in', function() {
+  describe('when the user is logged in', () => {
 
-    beforeEach(function (done) {
+    beforeEach((done) => {
       request.post({
         url: 'http://localhost:9000/login',
         form: { username: 'jose', password: 'Pa123' },
         json: true
-      }, function (err, resp, body) {
+      }, (err, resp, body) => {
         this.token = body.token;
         done();
-      }.bind(this));
+      });
     });
 
-    it('should do the handshake and connect', function (done) {
+    it('should do the handshake and connect', (done) => {
       io.connect('http://localhost:9000/admin', { forceNew: true })
-        .on('authenticated', done)
+        .on('authenticated', () => done())
         .emit('authenticate', { token: this.token });
     });
   });