add vendor & update README.md

vendor/github.com/gin-gonic/gin/response_writer_1.8.go

@@ -0,0 +1,25 @@
+// +build go1.8
+
+// Copyright 2018 Gin Core Team.  All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package gin
+
+import (
+	"net/http"
+)
+
+// ResponseWriter ...
+type ResponseWriter interface {
+	responseWriterBase
+	// get the http.Pusher for server push
+	Pusher() http.Pusher
+}
+
+func (w *responseWriter) Pusher() (pusher http.Pusher) {
+	if pusher, ok := w.ResponseWriter.(http.Pusher); ok {
+		return pusher
+	}
+	return nil
+}