Update tails-bugs@boum.org OpenPGP key

It expires on 2018-07-23 and we support upgrading from N-2 so we must ensure Tails 3.7 includes an updated key.

Feature Branch: bugfix/15534-update-tails-bugs-openpgp-key

Original created by @intrigeri on 15534 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information