Update react-scripts/create-react app

[zenlex]

The version of create-react-app we're built on is using react-scripts v2.1x which is well out of date and the source of most of our security audit issues. I don't think this is critical since we're not hosting or providing any secure information that isn't already publicly available but going forward if this app continues development it's probably worth an update. The changelog lists several potential breaking issues when jumping from 2.1x to 3.0 and beyond. Hopefully none that affect us, but given the short timeline to the 2020 election, figured best to not break it right now as it's not an urgent problem.