Switch to github.com/golang/dep for vendoring

Signed-off-by: Mrunal Patel <mrunalp@gmail.com>

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

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