BBR 1.15.0 deployment fails, but 1.18.9 succeeds

[kcboyle]

When we tried to deploy Concourse 7.3.0, we get the error on this Gist

The versions file for 7.3.0 (and most recent) looks like:

bbr_sdk_version: '1.15.0'
bbr_sdk_sha1: 'b2d8584dd2ed964c4849cb6d7b536e6cea3e6e8d'

When this is updated to the newest BBR:

bbr_sdk_version: '1.18.9'
bbr_sdk_sha1: '2b9713c7f2377a0c86495737dbdb5979bde9705d'

The deployment completes without error. Is this something y'all have hit? would you accept a PR to update this?