Fix checking gpg
    
    the command `gpgv` (Verify OpenPGP signatures) does not have
    parameter --no-default-keyring. That parameter is requried
    only for verify with gpg
    
    sh$ gpg2 --no-default-keyring --keyring ./tdb.keyring --verify ./tdb-1.4.3.tar.asc ./tdb-1.4.3.tar.gz
    gpg: Signature made Mon 16 Dec 2019 10:30:43 AM CET
    gpg:                using RSA key 9147A339719518EE9011BCB54793916113084025
    gpg:                issuer "samba-bugs@samba.org"
    gpg: BAD signature from "Samba Library Distribution Key <samba-bugs@samba.org>" [unknown]
    
    sh$ gpgv2 --keyring ./tdb.keyring ./tdb-1.4.3.tar.asc ./tdb-1.4.3.tar.gz
    gpgv: Signature made Mon 16 Dec 2019 10:30:43 AM CET
    gpgv:                using RSA key 9147A339719518EE9011BCB54793916113084025
    gpgv:                issuer "samba-bugs@samba.org"
    gpgv: BAD signature from "Samba Library Distribution Key <samba-bugs@samba.org>"