Activating bundler (~> 2.2) failed: Could not find 'bundler' (2.2.7) required by your /app/Gemfile.lock. at heroku

Question

I added build pack & Procfile. And so I tried to deploy to heroku. But error happened.

Idea

• I updated ruby 2.6.3 → 2.7.2 because heroku requires more hig