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/OAuth1.spec.js

@@ -1,4 +1,4 @@
-const OAuth = require("../src/Adapters/Auth/OAuth1Client");
+const OAuth = require("../lib/Adapters/Auth/OAuth1Client");
 
 describe('OAuth', function() {
   it("Nonce should have right length", (done) => {