Corret command to start a dev instance of Postgres.

Author: matthias_schaub

docs/source/dev_setup.md

@@ -60,7 +60,7 @@ Setup a local Postgres instance for MapSwipe Workers using the for development p
 
 ```bash
 cd postgres/`
-docker build -t mapswipe_postgres Dockerfile-dev
+docker build --tag mapswipe_postgres --file Dockerfile-dev .
 docker run -d -p 5432:5432 --name mapswipe_postgres -e POSTGRES_DB=mapswipe -e POSTGRES_USER=mapswipe_workers -e POSTGRES_PASSWORD=your_password mapswipe_postgres
 ```