Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

test/helpers/ether.js

@@ -1,3 +1,7 @@
-export default function ether (n) {
+function ether (n) {
   return new web3.BigNumber(web3.toWei(n, 'ether'));
 }
+
+module.exports = {
+  ether,
+};