www/writeas-cli: fix build on riscv64

The port asks for a version of golang.org/x/sys too old to
support riscv64-freebsd. Bump dependency to the current
v0.5.0 to fix the build.

MFH: 2023Q1
Sponsored by: Berliner Linux User Group e.V.
Approved by: eduardo (mentor)
Differential Revision: https://reviews.freebsd.org/D38680