Upgrade to Rails 6.1

Note that `Capybara.app_host` now returns `nil` by default and that
breaks tests using `lvh.me` or our custom `app_host` method, so we're
setting `Capybara.app_host` to the value it had in earlier versions of
Rails. I also haven't found a way to remove the code to set the
integration session host in relationable tests which I mentioned in
commit ffc14e499.

Also note that we now filter more parameters, and that they match
regular expressions, so filtering `:passw` means we're filtering
`passwd`, `password`, ...

bin/setup

@@ -9,8 +9,8 @@ def system!(*args)
 end
 
 FileUtils.chdir APP_ROOT do
-  # This script is a way to setup or update your development environment automatically.
-  # This script is idempotent, so that you can run it at anytime and get an expectable outcome.
+  # This script is a way to set up or update your development environment automatically.
+  # This script is idempotent, so that you can run it at any time and get an expectable outcome.
   # Add necessary setup steps to this file.
 
   puts "== Installing dependencies =="