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/cryptoUtils.spec.js

@@ -1,4 +1,4 @@
-const cryptoUtils = require('../src/cryptoUtils');
+const cryptoUtils = require('../lib/cryptoUtils');
 
 function givesUniqueResults(fn, iterations) {
   const results = {};