Bugfix: Mount app in app container instead of db container

docker-compose.override.yml

@@ -4,8 +4,9 @@ services:
   firefly-db:
     volumes:
       - firefly-dev-storage:/var/lib/mysql
-      - .:/var/www/firefly-iii
   firefly-app:
+    volumes:
+      - .:/var/www/firefly-iii
     environment:
       - INIT_DATABASE=yes
       - FF_APP_ENV=development