Merge branch 'pgdata' into 'master'

Use Docker volume for postgres data?

See merge request !14

docker-compose.yml

@@ -5,7 +5,7 @@ services:
     ports:
       - "5432:5432"
     volumes:
-      - ./postgres:/var/lib/postgresql/data
+      - pgdata:/var/lib/postgresql/data
   redis:
     image: 'redis:latest'
     ports:
@@ -44,3 +44,5 @@ volumes:
   gems:
     # Flagging this as "external" means it will use the volume named "gems" on the host instead of making a new volume specific to this docker-compose file
     external: true
+  pgdata:
+    external: true