Secure Boot: update grub and shim binaries
Quoting János Pásztor from https://github.com/grml/grml-live/pull/129:
After
581da7443c68c362a7677c905ab5c63eb23c5b73 and using the `debian`
style secure boot grml will not start on machines with secure boot
enabled, but fails with a `signature verification error`
After some investigation it turned out that we hit
https://bugs.debian.org/925550 with our boot binaries.
I have updated them from debian and managed to boot with them
properly.
While at it, switch from http://ftp.de.debian.org/ to
https://deb.debian.org/ which has proper SSL certificate available.
Thanks: János Pásztor <model87@freemail.hu> for bugreport and PR