I've been using this for years. I believe it only keeps one old kernel version though, not two like you requested. Tested and working for weekly use since 12.04 though 16.04:

echo $(dpkg --list | grep linux-image | awk '{ print $2 }' | sort | sed -n '/'`uname -r`'/q;p') $(dpkg --list | grep linux-headers | awk '{ print $2 }' | sort -n | sed -n '/'"$(uname -r | sed "s/\([0-9.-]*\)-\([^0-9]\+\)/\1/")"'/q;p') | xargs sudo apt-get -y purge

This is the new way to do it:

    sudo purge-old-kernels --keep 3 -qy

TIL