Update dependencies

[lognaturel]

Makes progress towards #440 Closes #441

What has been done to verify that this works as intended?

pyxform: converted a form with list_name on entities sheet to verify the latest version is used

postgres: clicked around on dev server

redis: opened a few forms on dev server

smtp: this one was the most annoying. There's nothing particularly significant in the changelog but I still wanted to verify it. In this process, I discovered that Digital Ocean now blocks SMTP. I pulled @yanokwa in. We verified exim logs inside the container to make sure messages were being queued in the same way as with prior versions. He also verified that https://www.mail-tester.com/ gets email delivered. In doing all this he discovered some DKIM-related bugs that he'll follow up on. @yanokwa will submit a separate PR for this update.

Why is this the best possible solution? Were any other approaches considered?

I checked all docker files and docker-compose for versions to update. I believe this is exhaustive.

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

I don't see much risk after the verification above.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

No.

Before submitting this PR, please make sure you have:

• verified that any code or assets from external sources are properly credited in comments or that everything is internally sourced

[matthew-white]

It might be nice to update this in the Backend CircleCI config so that we're certain that Backend tests run successfully against the version of Postgres that we ship. Probably not a big deal though: it'd be pretty surprising if anything failed.