Upgrade gin-gonic to latest master, fix compatibility issues

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

@@ -0,0 +1,36 @@
+// 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 (
+	"fmt"
+	"io"
+	"net/http"
+)
+
+type String struct {
+	Format string
+	Data   []interface{}
+}
+
+var plainContentType = []string{"text/plain; charset=utf-8"}
+
+func (r String) Render(w http.ResponseWriter) error {
+	WriteString(w, r.Format, r.Data)
+	return nil
+}
+
+func (r String) WriteContentType(w http.ResponseWriter) {
+	writeContentType(w, plainContentType)
+}
+
+func WriteString(w http.ResponseWriter, format string, data []interface{}) {
+	writeContentType(w, plainContentType)
+	if len(data) > 0 {
+		fmt.Fprintf(w, format, data...)
+	} else {
+		io.WriteString(w, format)
+	}
+}