Upgrade dotenv and dotenv-expand to latest version

Created by: ericrallen

The 5.*.* release of dotenv-expand fixes a bug where ENV variables set in the CLI as empty were getting overwritten by values in .env files, this bug was previously fixed in dotenv, but the fix was not ported over to dotenv-expand until recently.

It also adds better support for ENV variable values with $s in them and better handling of escaped $s in values.

I went ahead and updated dotenv to the latest version, as well. I believe the major version bump was just to drop support for older versions of Node.