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/PushController.spec.js

@@ -1,8 +1,8 @@
 "use strict";
-const PushController = require('../src/Controllers/PushController').PushController;
-const StatusHandler = require('../src/StatusHandler');
-const Config = require('../src/Config');
-const validatePushType = require('../src/Push/utils').validatePushType;
+const PushController = require('../lib/Controllers/PushController').PushController;
+const StatusHandler = require('../lib/StatusHandler');
+const Config = require('../lib/Config');
+const validatePushType = require('../lib/Push/utils').validatePushType;
 
 const successfulTransmissions = function(body, installations) {