I tried running:
$ git push heroku master
-----
Total 7121 (delta 2300), reused 6879 (delta 2228)
! Heroku push rejected, no Cedar-supported app de
Just had this problem too. I did the following to solve it: (assuming you're in project dir)
rm -rf .git
git init
git add .
git commit -m "First commit"
heroku create --stack cedar
git push heroku master
A slightly involved solution to create a new application, but at least it works. Hope that helps!