update go-github dependency

closes #42

vendor/github.com/google/go-github/github/with_appengine.go

@@ -0,0 +1,26 @@
+// Copyright 2017 The go-github AUTHORS. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build appengine
+
+// This file provides glue for making github work on App Engine.
+// In order to get the entire github package to compile with
+// Go 1.6, you will need to rewrite all the import "context" lines.
+// Fortunately, this is easy with "gofmt":
+//
+//     gofmt -w -r '"context" -> "golang.org/x/net/context"' *.go
+
+package github
+
+import (
+	"context"
+	"net/http"
+
+	"google.golang.org/appengine"
+)
+
+func withContext(ctx context.Context, req *http.Request) (context.Context, *http.Request) {
+	return appengine.WithContext(ctx, req), req
+}