Upgrade webpacker

[bess]

Following instructions on https://github.com/rails/webpacker#upgrading

[coveralls]

Coverage remained the same at 99.636% when pulling c7aa3b7 on upgrade-webpacker into 8d72b70 on main.

[eliotjordan]

@bess There is something wrong with the javascript on this branch. I haven’t taken a close look, but If you open the browser console when loading the app you’ll see what I mean. An error in geo-coder.js and results.js.