Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

test/helpers/decodeLogs.js

@@ -1,8 +1,12 @@
 const SolidityEvent = require('web3/lib/web3/event.js');
 
-export default function decodeLogs (logs, contract, address) {
+function decodeLogs (logs, contract, address) {
   return logs.map(log => {
     const event = new SolidityEvent(null, contract.events[log.topics[0]], address);
     return event.decode(log);
   });
 }
+
+module.exports = {
+  decodeLogs,
+};