Fix Node.js v6 tests
Fix Node.js v6 tests

In nodejs/node@20285ad177551 [1], the error message
for passing an invalid argument to EventEmitter.setMaxListeners
was changed, which this module explicitly tests for.

This fixes this test when using the current Node.js master branch.

[1]: https://github.com/nodejs/node/commit/20285ad177551

yanickrochon/promise-events