Comment 22 for bug 1587975

As point it out in several comments , fixing the missing GPG solved the problem for me .
In my case was the new skype version :

# make sure you have 'apt-transport-https' installed
dpkg -s apt-transport-https > /dev/null || bash -c "sudo apt-get update; sudo apt-get install apt-transport-https -y"
curl https://repo.skype.com/data/SKYPE-GPG-KEY | sudo apt-key add -
echo "deb [arch=amd64] https://repo.skype.com/deb stable main" | sudo tee /etc/apt/sources.list.d/skype-stable.list
sudo apt-get update
sudo apt-get install skypeforlinux -y