bug #804 Removed Heroku support (javiereguiluz)

This PR was merged into the master branch.

Discussion
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Removed Heroku support

This fixes #755. Sadly, Heroku support has been broken for months, so let's remove it. Once we add full Docker support for this project, it may be easier to reintroduce Heroku support.

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3359073 Removed Heroku support

Author: javiereguiluz

README.md

@@ -20,8 +20,6 @@ Execute this command to install the project:
 $ composer create-project symfony/symfony-demo
 ```
 
-[![Deploy](https://www.herokucdn.com/deploy/button.png)](https://heroku.com/deploy)
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