openwrt-keyring: update to Git HEAD

openwrt-keyring: update to Git HEAD

8080ef3 usign: add 19.07 release build pubkey
e24fe0d usign: use distro agnostic comments
251ded7 usign: fix filename of Stijn's usign key
14f0efc gpg: update snapshots public signing key
14f845b gpg: replace my public GPG key
4f735b8 gpg: add OpenWrt 19.07 signing key
228f8da gpg: add OpenWrt 18.06 v2 signing key
36057d9 gpg: update LEDE 17.01 public signing key
f2989ab Add my public GPG and usign key

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit e9216b3336f7a774be7021dd663a433d9ec5edc7)