Simplify the sanity test check

App doesn't need to listen in the test script as supertest accepts the
app variable and handles the listening and un-listening itself.

This also removes the needs for the after block to stop the server.

test/spec/sanity-checks.js

@@ -1,20 +1,14 @@
-/* global describe, it, before */
+/* eslint-env mocha */
 var request = require('supertest')
-var assert = require('assert')
+var app = require('../../server.js')
 var path = require('path')
 var fs = require('fs')
+var assert = require('assert')
 
 /**
  * Basic sanity checks on the dev server
  */
 describe('The prototype kit', function () {
-  var app
-
-  before(function (done) {
-    app = require('../../server')
-    done()
-  })
-
   it('should generate assets into the /public folder', function () {
     assert.doesNotThrow(function () {
       fs.accessSync(path.resolve(__dirname, '../../public/javascripts/application.js'))
@@ -27,6 +21,13 @@ describe('The prototype kit', function () {
     request(app)
       .get('/')
       .expect('Content-Type', /text\/html/)
-      .expect(200, done)
+      .expect(200)
+      .end(function (err, res) {
+        if (err) {
+          done(err)
+        } else {
+          done()
+        }
+      })
   })
 })