Upgrade gin-gonic to latest master, fix compatibility issues

vendor/github.com/gin-gonic/gin/render/xml.go

@@ -0,0 +1,25 @@
+// Copyright 2014 Manu Martinez-Almeida.  All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+package render
+
+import (
+	"encoding/xml"
+	"net/http"
+)
+
+type XML struct {
+	Data interface{}
+}
+
+var xmlContentType = []string{"application/xml; charset=utf-8"}
+
+func (r XML) Render(w http.ResponseWriter) error {
+	r.WriteContentType(w)
+	return xml.NewEncoder(w).Encode(r.Data)
+}
+
+func (r XML) WriteContentType(w http.ResponseWriter) {
+	writeContentType(w, xmlContentType)
+}