www/websocketd: Fix make fetch

The go version is missing in the go.mod of released version.
The fix is unreleased yet.

Reference: https://github.com/joewalnes/websocketd/commit/0aa12c3913f5b86e15c232e4191a6ef1953a354f
(cherry picked from commit 24005c6c4bf0aa38ea22acbfcd08b630ca94a3f8)