Occasional Puppeteer test failures

[WesCossick]

The Puppeteer tests will sometimes fail, which is fixed by simply retrying. I added a wait option, but that did not fix the issue. We need to look into why this is, because it's confusing Greenkeeper and making our workflow more inefficient.

Here's some examples:

Testing has failed on both Node.js LTS and current. I'm currently seeing if it's always the same test case.

[WesCossick]

I have re-run the build on master many times and have not been able to get this error to crop up again. We've seen it occur a few times already in the past, though, spread over multiple days.

[WesCossick]

I’m going to assume that the changes in #51 fixed this problem, but will reopen this issue if it crops up again.