vendor: sirupsen/logrus -> Sirupsen/logrus

github.com/docker/docker/pkg/archive requires Sirupsen/logrus.
So let's remove sirupsen/logrus at the moment.

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

vendor/github.com/sirupsen/logrus/terminal_appengine.go

@@ -1,8 +0,0 @@
-// +build appengine
-
-package logrus
-
-// IsTerminal returns true if stderr's file descriptor is a terminal.
-func IsTerminal() bool {
-	return true
-}