cmd/tailscale: s/-authkey/-auth-key/ in help text
If flags are specified, the flags must be the complete set of desired
settings. An error is returned if any setting would be changed as a
result of an unspecified flag's default value, unless the --reset flag
-is also used. (The flags --authkey, --force-reauth, and --qr are not
+is also used. (The flags --auth-key, --force-reauth, and --qr are not
considered settings that need to be re-specified when modifying
settings.)
`),
