cmd/tailscale/cli: [ssh] fix typo in help text
arugments => arguments
The 'tailscale ssh' wrapper adds a few things:
-* It resolves the destination server name in its arugments using MagicDNS,
+* It resolves the destination server name in its arguments using MagicDNS,
even if --accept-dns=false.
* It works in userspace-networking mode, by supplying a ProxyCommand to the
system 'ssh' command that connects via a pipe through tailscaled.
