Promisify web3 sync requests in tests (#1009)

test/helpers/latestTime.js

@@ -1,4 +1,7 @@
+import { ethGetBlock } from './web3';
+
 // Returns the time of the last mined block in seconds
-export default function latestTime () {
-  return web3.eth.getBlock('latest').timestamp;
+export default async function latestTime () {
+  const block = await ethGetBlock('latest');
+  return block.timestamp;
 }