Fix date/time localization

docker-compose.yml.example

@@ -8,6 +8,8 @@ services:
       - 5000:5000
     environment:
       - FABCAL_CACHE_EXPIRE=120
+      - LANG=de
+      - LC_ALL=de_DE.UTF-8
     volumes:
       - ./config.yml:/app/config.yml:ro
     # use the line below when running this behind reverse proxy (only if it sets the proxy headers, though)