Merge pull request #3669 from chrisclark/master

Docs: Typo leading to possible extreme agony
(cherry picked from commit edd3637b9b)
Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>

docs/compose-file.md

@@ -789,7 +789,7 @@ called `data` and mount it into the `db` service's containers.
       db:
         image: postgres
         volumes:
-          - data:/var/lib/postgres/data
+          - data:/var/lib/postgresql/data
 
     volumes:
       data: