Patch test compose file to specify required vars

Author: rjhenry

docker-compose.test.yml

@@ -21,6 +21,7 @@ services:
     - mysql
     environment:
     - APP_URL=http://localhost:${DEV_PORT:-8080}
+    - APP_KEY=SomeRandomString
     - DB_HOST=mysql:3306
     - DB_DATABASE=bookstack
     - DB_USERNAME=bookstack