Update docker-compose.yaml (#3582)

The following error gets returned when trying to launch
langchain-server:

ERROR: The Compose file
'/opt/homebrew/lib/python3.11/site-packages/langchain/docker-compose.yaml'
is invalid because:
services.langchain-db.expose is invalid: should be of the format
'PORT[/PROTOCOL]'

Solution:
Change line 28 from - 5432:5432 to - 5432

langchain/docker-compose.yaml

@@ -26,4 +26,4 @@ services:
       - POSTGRES_USER=postgres
       - POSTGRES_DB=postgres
     expose:
-      - 5432:5432
+      - 5432