Changes docker network size to valid for docker compose

[roundowl]

Docker compose plugin can't start using these configs because the network 10.20.20.0/16 is invalid and it expects either 10.20.0.0/16 or 10.20.20.0/24. Since we're using only up to five addresses and change only 4th octet, it's more viable to change the network to /24.

Relevant issue: #602

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