update problem in fedora 28 in cinnamon :
warning: /var/cache/dnf/google-talkplugin-dfa34928d410c534/packages/google-talkplugin-5.41.3.0-1.x86_64.rpm:
Header V4 DSA/SHA1 Signature, key ID 7fac5991: NOKEY
Public key for google-talkplugin-5.41.3.0-1.x86_64.rpm is not installed
The downloaded packages were saved in cache until the next successful transaction.
You can remove cached packages by executing 'dnf clean packages'.
Error: GPG check FAILED
