post_upgrade() {
    if [ $(vercmp $2 2.1.1-1) -lt 0 ] ; then
        cat << EOF

Be sure to read http://docs.couchdb.org/en/2.1.1/whatsnew/2.1.html#upgrade-notes.
Note that your /etc/couchdb/vm.args has been replaced by the new one if you
never edited it, so you might actually have to change it as advised.

EOF
    fi
}