Fixed environmental variables

Dockerfile_db

@@ -1,5 +1,9 @@
 FROM postgres:12.0-alpine
 
+ARG PACKMATE_DB_USER
+ARG PACKMATE_DB_PASSWORD
+ARG PACKMATE_DB_DB
+
 ENV POSTGRES_USER ${PACKMATE_DB_USER:-packmate}
 ENV POSTGRES_PASSWORD ${PACKMATE_DB_PASSWORD:-packmate_secret_password}
 ENV POSTGRES_DB ${PACKMATE_DB_DB:-packmate}