Drop Go 1.3 support

modules/ssh/ssh.go

@@ -1,5 +1,3 @@
-// +build go1.4
-
 // Copyright 2014 The Gogs Authors. All rights reserved.
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.

modules/ssh/ssh_1.3.go

@@ -1,7 +0,0 @@
-// +build !go1.4
-
-package ssh
-
-func Listen(port int) {
-	panic("Gogs requires Go 1.4 for starting a SSH server")
-}