net/dns: fix typo in docstring.
// An OSConfigurator applies DNS settings to the operating system.
type OSConfigurator interface {
// Set updates the OS's DNS configuration to match cfg.
- // If cfg nil or the zero value, all Tailscale-related DNS
+ // If cfg is the zero value, all Tailscale-related DNS
// configuration is removed.
// Set must not be called after Close.
Set(cfg OSConfig) error
