cmd/prober: update check from "Go Discovery" to "go.dev"
cmd/prober: update check from "Go Discovery" to "go.dev"

Fixes b/144301072

Change-Id: I1929bf25877e543c111fc1276ff60b83d280a524
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/596762
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite