Fix console.warn in truffle test

Author: Kenadia

packages/core/lib/test.js

@@ -58,7 +58,7 @@ const Test = {
  // e.g., https://github.com/ethereum/web3.js/blob/master/lib/web3/allevents.js#L61
  // Output looks like this during tests: https://gist.github.com/tcoulter/1988349d1ec65ce6b958
  const warn = config.logger.warn;
- config.logger.warn = message => {
+ config.logger.warn = function(message) {
  if (message === "cannot find event for log") {
  return;
  } else {