heruko ruby on rails: push rejected no cedar supported app detected

Today I am trying to deploy my ruby on rails app into heruko.
But got an error when I am trying to use  git push heruko master
What I did:
git clone an existing app that is completed
then do everything as the tutorial said 

but got this error
 
What to do?
It seems that the old .git information has some bad effect on deploying
So
here is the solution:
rm -rf .git
git init
git add .
git commit -am "Reinitialize"
heroku create --stack cedar
git push heroku master
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