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/MongoStorageAdapter.spec.js

@@ -1,6 +1,6 @@
 'use strict';
 
-import MongoStorageAdapter from '../src/Adapters/Storage/Mongo/MongoStorageAdapter';
+const MongoStorageAdapter = require('../lib/Adapters/Storage/Mongo/MongoStorageAdapter').default;
 const { MongoClient } = require('mongodb');
 const databaseURI = 'mongodb://localhost:27017/parseServerMongoAdapterTestDatabase';