gems: update rubocop to version 0.81.0
gems: update rubocop to version 0.81.0

(#3)
Co-authored-by: depfu[bot] <2714779d9417fc52c071749b76ce00064c1f90e7@users.noreply.github.com>
cmur2/openvpn-status-web,cmur2/openvpn-status-web