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

.nycrc

@@ -5,7 +5,7 @@
   ],
   "exclude": [
     "**/spec/**",
-    "lib/"
+    "src/"
   ]
 }