bug #643 Update env variables for the heroku deployment (stof)

This PR was merged into the master branch.

Discussion
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Update env variables for the heroku deployment

I have not updated the SYMFONY_LOG one, as the monolog config does not use an env variable anymore for the log output, so it requires more work.

Commits
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f08d805 Update env variables for the heroku deployment

Author: javiereguiluz

app.json

@@ -15,12 +15,15 @@
         "test": "phpunit"
     },
     "env": {
-        "SYMFONY_ENV": {
+        "APP_ENV": {
             "value": "prod",
             "description": "If you want to use the Symfony `dev` environment in the deployed application, you must move the necessary dependencies (like SensioGeneratorBundle) from `require-dev` to `require`. This will introduce security issues because development tools like the WebProfiler reveal sensitive information."
         },
+        "APP_DEBUG": {
+            "value": "0"
+        }
         "SYMFONY_LOG": "php://stderr",
-        "SYMFONY_SECRET": {
+        "APP_SECRET": {
             "description": "Extra entropy for %kernel.secret%; used for CSRF tokens, cookies and signed URLs.",
             "generator": "secret"
         }