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

.babelrc

@@ -9,5 +9,6 @@
                 "node": "8"
             }
         }]
-    ]
+    ],
+    "sourceMaps": "inline"
 }