www/pomerium: fix build on riscv64

Bump golang.org/x/sys dependency to a version new enough
to support riscv64-freebsd. While we are at it, chase
github.com/go-redis/redis -> github.com/redis/go-redis rename.

Sponsored by: Berliner Linux User Group e.V.
Approved by: portmgr (build fix blanket)