chore(ci): Replace Snyk with yarn audit

[hedgepigdaniel]

Snyk is really resisting being used for free. Meanwhile yarn audit is much simpler to use.

I upgraded packages to fix all the identified vulnerabilities, which required some babel+jest fixes to account for the breaking changes in jest.

I removed the vulnerability checking from the CI script for 2 reasons:

• It doesn't work because Travis has too old a version of yarn
• Its non-deterministic, and it doesn't make sense to block PRs because a new unrelated vulnerability was found. For example refactor: 💡 Add options to the "call" middleware #17 is totally unrelated to Snyk and yet it hasn't been merged because of Snyk.