Unable to use Docker Compose 3.5 Features - docker

Question

So I'm trying to setup some docker-compose scripts using some of the latest compose 3.5 features. The big one is being able to name networks. So there are some containers that I end up reproducing over and over again, such as a Postgres database, with various apps I work on. My goal is to be able to have a docker-compose script for something like Postgres, with a named network, which I can then have other apps with their own docker-compose scripts just add on to. It feels more re-usable that way.
Anyway, here is the docker-compose script I'm working with:
version: '3.5'
services:
postgres:
image: postgres:11
container_name: postgres
networks:
- pg_network
environment:
- POSTGRES_PASSWORD=password
- POSTGRES_USER=user
ports:
- 5432:5432
volumes:
- ~/.postgresql/data:/var/lib/postgresql/data
- ~/.postgresql/init:/docker-entrypoint-initdb.d
pgadmin:
image: dpage/pgadmin4
container_name: pgadmin
networks:
- pg_network
ports:
- 5433:80
environment:
- PGADMIN_DEFAULT_EMAIL=user#gmail.com
- PGADMIN_DEFAULT_PASSWORD=password
volumes:
- ~/.postgresql/pgadmin:/var/lib/pgadmin
networks:
pg_network:
name: pg_network
I am trying to use the "custom name" feature new in Docker Compose 3.5. See this link for the documentation: https://docs.docker.com/compose/networking/
However, when I try to run docker-compose up -d, I get the following error:
ERROR: The Compose file './docker-compose.yml' is invalid because:
networks.pg_network value Additional properties are not allowed ('name' was unexpected)
I'm not sure what I'm doing wrong. I'm on Ubuntu 18.04, I'm running the docker commands with sudo (because that seems to be a requirement on Ubuntu).
Here are my Docker and Docker Compose versions:
Docker version 18.09.2, build 6247962
docker-compose version 1.17.1, build unknown
I've tried upgrading them with APT, but it says they are up to date.
So, either I'm making a mistake in my compose script, or there's something screwy with my Docker version. I would appreciate any insight that can be offered. Thank you.