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/PushQueue.spec.js

@@ -1,5 +1,5 @@
-import Config from "../src/Config";
-import {PushQueue} from "../src/Push/PushQueue";
+const Config = require("../lib/Config");
+const {PushQueue} = require("../lib/Push/PushQueue");
 
 describe('PushQueue', () => {
   describe('With a defined channel', () => {