Run CI against Go 1.15 NO CHANGELOG
Go 1.15 has been out for a long time, and 1.16 will be released soon. We'll need to remove 1.13 when that happens, but in the meantime, let's make sure we work on 1.15
We're building against 1.14 for deployment so there's no particular urgency to this.
Part of #324
Edited by Nick Thomas