Removes need to use babel-register (#4865)

* Removes need to use babel-register

- Adds watch to watch changes when running the test to regenerate
- Tests are now pure node 8

* Adds timing to helper.js

* Update contribution guide

* Adds inline sourcemaps generation to restore coverage

* nits

spec/HTTPRequest.spec.js

@@ -1,7 +1,7 @@
 'use strict';
 
-const httpRequest = require("../src/cloud-code/httpRequest"),
-  HTTPResponse = require('../src/cloud-code/HTTPResponse').default,
+const httpRequest = require("../lib/cloud-code/httpRequest"),
+  HTTPResponse = require('../lib/cloud-code/HTTPResponse').default,
   bodyParser = require('body-parser'),
   express = require("express");