heroku: make env var customizable

app.json

@@ -1 +1,17 @@
-{"stack": "container"}
+{
+	"stack": "container",
+	"env": {
+		"DEBUG": {
+			"value": 1,
+			"required": false
+		},
+		"CACHE": {
+			"value": "diskcache",
+			"required": false
+		},
+		"CACHE_SIZE": {
+			"value": 1073741824,
+			"required": false
+		}
+	}
+}

heroku.yml

@@ -1,9 +1,3 @@
-setup:
-  config:
-    DEBUG: 1
-    CACHE: diskcache
-    CACHE_SIZE: 1073741824
-
 build: 
   docker:
     web: Dockerfile