Playwright: the re-wright

[adroitwhiz]

Resolves

Resolves #564
Resolves #601

Proposed Changes

This is #597, but with some extra stuff to fix Travis:

• Cache ~/.cache/ms-playwright in Travis so that the downloaded Chromium binary always exists
• Exit the tests with process exit code 1 if a promise throws an error, so that builds do not pass if an error occurs when testing

Reason for Changes

See #597

Test Coverage

Yes

[cwillisf]

👍 thanks for the extra attention to error handling!