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/PostgresStorageAdapter.spec.js

@@ -1,4 +1,4 @@
-import PostgresStorageAdapter from '../src/Adapters/Storage/Postgres/PostgresStorageAdapter';
+const PostgresStorageAdapter = require('../lib/Adapters/Storage/Postgres/PostgresStorageAdapter').default;
 const databaseURI = 'postgres://localhost:5432/parse_server_postgres_adapter_test_database';
 
 const getColumns = (client, className) => {