apt-get update devuelve: W: GPG error: http://pl.archive.ubuntu.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32 W: GPG error: http://pl.archive.ubuntu.com trusty-updates Release: The...