deploy can fail with SSH fingerprint confirmation

See for instance https://travis-ci.com/Quansight/lsst_dashboard/jobs/263181340

```
git fetch doctr_remote
The authenticity of host 'github.com (192.30.253.112)' can't be established.
RSA key fingerprint is SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8.
Are you sure you want to continue connecting (yes/no)?
```