x11-wm/river: update to 0.1.0

Changes: https://github.com/ifreund/river/compare/8134b81...v0.1.0
Changes: https://github.com/riverwm/river/releases/tag/v0.1.0
Reported by: GitHub (watch releases)

(cherry picked from commit bc0ed5080dcde2729c19f3a6bc04b7225117846d)