Remove Redis (Heroku) Support?

[nelsonic]

We are no longer using Heroku for this project
because heroku is (much more) expensive and slow(er) than Linode!
While I still want this to be a useful learning project for beginners
I don't think beginners are going to actually run the project on Heroku ...

If anyone wants to run it on Heroku they can use the Redis version:
https://github.com/dwyl/hits/tree/4f5d73fcc1a3b1f7e0c6dd39d53d19c1fa49761f