Swap node versions in our CI tests

[jeffposnick]

R: @philipwalton

Fixes #2443

[jeffposnick]

So in this PR, our macOS CI tests are now failing with

[14:41:44] 'test-integration' errored after 11 min
[14:41:44] Error: Server terminated early with status 1
    at /Users/runner/runners/2.168.0/work/workbox/workbox/node_modules/selenium-webdriver/remote/index.js:251:52
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
[14:41:44] 'test' errored after 17 min

right at the point where the first Safari test should start, after the Firefox tests complete. Investigating further...

[jeffposnick]

I can reproduce the Error: Server terminated early with status 1 error when testing against Safari while running the test suite for the underlying selenium-assistant library. Upgrading to selenium-webdriver ^4.0.0-alpha.7 in that underlying library didn't help, either.

Still investigating, but it does appear to be more of an issue with the testing infrastructure in general and less with anything we're doing in our tests.

[jeffposnick]

Okay, it's due to https://github.com/GoogleChromeLabs/selenium-assistant/blob/92a799db2025b08bc698a9bcf84f61e5d4142638/src/local-browsers/safari.js#L64-L69, which was a workaround for Safari >= 12 that doesn't appear to be necessary anymore in Safari 13.1.

I am going to push out a new release of selenium-assistant that changes that logic so that it's not in effect for Safari 13.1, and then hopefully the tests will work moving forward.

[jeffposnick]

...now Windows is failing due to npm/cli#558

Fun. There are some workarounds in that thread.

[jeffposnick]

Okay! That's better.