Use 127.0.0.1 for ssh tunnel

The previous 'localhost' value was causing connection problems on the
remote host, such that it would not create a connection through the
tunnel to the specified port.

lib/kamal/cli/port_forwarding.rb

@@ -26,10 +26,10 @@ class Kamal::Cli::PortForwarding
 		@threads = hosts.map do |host|
 			Thread.new do
 				Net::SSH.start(host, KAMAL.config.ssh.user) do |ssh|
-					ssh.forward.remote(port, "localhost", port, "localhost")
+					ssh.forward.remote(port, "127.0.0.1", port)
 					ssh.loop(0.1) do
 						if @done
-							ssh.forward.cancel_remote(port, "localhost")
+							ssh.forward.cancel_remote(port)
 							break
 						else
 							true