build: send build fail/pass notifications to mailing list
build: send build fail/pass notifications to mailing list

Bring this repo in line with the main repo.

Change-Id: I54d826e8287f6c461d0b07830dfc72c39b3c44b0
Reviewed-on: https://upspin-review.googlesource.com/13121
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

upspin/aws