docker-compose.yml: `version` is obsolete

[dckc]

This version thing is evidently obsolete:

dapp-agoric-basics/docker-compose.yml

Line 1 in 3c28a51

version: '3.5'

I ran across the diagnostic again while looking at ci for #59:

time="2024-09-03T16:25:29Z" level=warning msg="/home/runner/work/dapp-agoric-basics/dapp-agoric-basics/docker-compose.yml: `version` is obsolete"

-- https://github.com/Agoric/dapp-agoric-basics/actions/runs/10686773433/job/29622821635?pr=59#step:8:16

This is another case of...

• how to keep in sync with dapp-offer-up? #4

We fixed it already in dapp-offer-up:

Agoric/dapp-offer-up@8935354

the orch dapp has the same problem:
https://github.com/Agoric/dapp-orchestration-basics/blob/b71ad31d32d87314aea508e68478b0a256ce43d9/docker-compose.yml#L1