Mass updates

[dfreeman]

This gets the vast majority of our dependencies up to date, with a few changes (like updating prettier) pulled into their own commits for clarity. I'm hoping to get the Renovate traffic jam cleared out.

[dfreeman]

Before merging this, we may want to create a v3 branch off master. Several of these updates require Node 10, which is already what we're running CI against, but 3.x officially supports Node 8 still.

[dfreeman]

For future travelers: we decided to create any potential v3 branch based on our last 3.x tag rather than from master to be sure we don't accidentally include something that depends on Node 10 that got Renovated in in the meantime.