Not working on Heroku-18 Stack

[mayordwells]

Please when can you help get this to work on Heroku-18 stack?
When I checked my stack, it showed this:
ndt-nordvest (master) $ heroku stack
=== ⬢ ndt-nordvest Available Stacks
cedar-14
container
heroku-16

• heroku-18

Thank you.

[rposborne]

This is a duplicate of #37 closing in favor of that issue