Fix copypasta

terminal_appengine.go

@@ -1,5 +1,5 @@
 // Based on ssh/terminal:
-// Copyright 2013 The Go Authors. All rights reserved.
+// Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -7,5 +7,7 @@
 
 package logrus
 
+import "io"
+
 func initTerminal(w io.Writer) {
 }