[hotfix] repair backup script

• SYMPTOM: backup script was not depositing backups on backup server
• CAUSE: around 2020-08-06, we introduced a change to the docker-compose file that exposed ports based on env vars. the backup up pg_dump aliases do not provide the --env-file flag, and as such, these directives are invalid and the docker-compose file fails to parse
• FIX: provide --env-file .env in both the up and pg_dump directives

future mitigation thought:

• it doesn't actually seem all that helpful to provide these ports as env vars... maybe just inline them in the docker config? and if we want a single source of truth, then use yaml anchors?