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/parsers.spec.js

@@ -1,4 +1,4 @@
-import {
+const {
   numberParser,
   numberOrBoolParser,
   booleanParser,
@@ -6,7 +6,7 @@ import {
   arrayParser,
   moduleOrObjectParser,
   nullParser,
-} from '../src/Options/parsers';
+} = require('../lib/Options/parsers');
 
 describe('parsers', () => {
   it('parses correctly with numberParser', () => {