Update vendors.

Signed-off-by: Lantao Liu <lantaol@google.com>

vendor/github.com/docker/spdystream/utils.go

@@ -0,0 +1,16 @@
+package spdystream
+
+import (
+	"log"
+	"os"
+)
+
+var (
+	DEBUG = os.Getenv("DEBUG")
+)
+
+func debugMessage(fmt string, args ...interface{}) {
+	if DEBUG != "" {
+		log.Printf(fmt, args...)
+	}
+}