Remove Babel (#1074)

* Test helpers no longer rely on Babel.

* Behaviours are no longer imported.

* Removed Babel dependency.

* Fixed linter errors.

test/helpers/advanceToBlock.js

@@ -1,4 +1,4 @@
-export function advanceBlock () {
+function advanceBlock () {
   return new Promise((resolve, reject) => {
     web3.currentProvider.sendAsync({
       jsonrpc: '2.0',
@@ -11,7 +11,7 @@ export function advanceBlock () {
 }
 
 // Advances the block number so that the last mined block is `number`.
-export default async function advanceToBlock (number) {
+async function advanceToBlock (number) {
   if (web3.eth.blockNumber > number) {
     throw Error(`block number ${number} is in the past (current is ${web3.eth.blockNumber})`);
   }
@@ -20,3 +20,8 @@ export default async function advanceToBlock (number) {
     await advanceBlock();
   }
 }
+
+module.exports = {
+  advanceBlock,
+  advanceToBlock,
+};