x11/rofi-calc: update to 2.3.1

Changes:
Specify mode type to get rid of a warning message, PR #134
https://github.com/svenstaro/rofi-calc/pull/134

Changelog: https://github.com/svenstaro/rofi-calc/blob/v2.3.1/CHANGELOG.md

PR: 287381
Reported by: Vidar Karlsen <vidar@karlsen.tech> (maintainer)