How to cancel redundant builds on Heroku Review-app

Question

I want to start building the old review apps only with the current changes on the PRs I have.

Current behaviour:

1. After a push to the PR heroku start building the review app.
2. After another change is pushed to the PR heroku enqueue another build but it does not stop the build from 1.

I cant find a way to setup this, how can I do it?