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### Summary

When using the latest docker image, the port set in the connection string seems to get lost somehow. The rest of the connection string is parsed fine.

### Steps to reproduce

This seems to be consistently reproducable with the `latest` docker image:
```
docker run --rm -it -p 5000:5000 graphile/postgraphile --connection 'postgres://some:user@172.17.0.1:9193/somedb'
```

### Expected results

Expected is either a connection, or at least an error connecting to port 9193. Expected:

```
PostGraphile v4.12.1 server listening on port 5000 🚀

  ‣ GraphQL API:         http://0.0.0.0:5000/graphql
  ‣ GraphiQL GUI/IDE:    http://0.0.0.0:5000/graphiql (RECOMMENDATION: add '--enhance-graphiql')
  ‣ Postgres connection: postgres://some:[SECRET]@172.17.0.1:9193/somedb
  ‣ Postgres schema(s):  public
  ‣ Documentation:       https://graphile.org/postgraphile/introduction/
  ‣ Node.js version:     v12.22.1 on linux x64
  ‣ Join Splitgraph in supporting PostGraphile development: https://graphile.org/sponsor/

* * *

```
This output was captured with the same command as above, but I added `-e "PGPORT=9193"`. After this addition postgraphile works as expected.

### Actual results

```
PostGraphile v4.12.1 server listening on port 5000 🚀

  ‣ GraphQL API:         http://0.0.0.0:5000/graphql
  ‣ GraphiQL GUI/IDE:    http://0.0.0.0:5000/graphiql (RECOMMENDATION: add '--enhance-graphiql')
  ‣ Postgres connection: postgres://some:[SECRET]@172.17.0.1/somedb
  ‣ Postgres schema(s):  public
  ‣ Documentation:       https://graphile.org/postgraphile/introduction/
  ‣ Node.js version:     v12.22.1 on linux x64
  ‣ Join Chris Watland in supporting PostGraphile development: https://graphile.org/sponsor/

* * *

A serious error occurred when building the initial schema. Exiting because `retryOnInitFail` is not set. Error details:

Error: connect ECONNREFUSED 172.17.0.1:5432
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1144:16)
```

### Additional context

About 7 months ago this used to work as expected. It seems like somehow the port is lost from the connection string, especially since setting the `PGPORT` env var connects on the right postgres port