Switch to dep for dependency management

vendor/github.com/gin-gonic/gin/context_appengine.go

@@ -1,5 +1,9 @@
 // +build appengine
 
+// Copyright 2017 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 gin
 
 func init() {