We don't want to force ourselves to update the DERP list
every time we want to cut a new release.
Having an outdated DERP list on release branches is OK.
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
In prep for using 1.17 features.
Note the go.mod changes are due to:
https://golang.org/doc/go1.17#go-command
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>