Fix for this App Engine Go issue: https://code.google.com/p/googleappengine/issues/detail?id=12725

fix-golang-ctxhttp-on-appengine-sdk-1.36+.diff

diff --git a/vendor/golang.org/x/net/context/ctxhttp/cancelreq.go b/vendor/golang.org/x/net/context/ctxhttp/cancelreq.go
index 48610e3..214fbaf 100644
--- a/vendor/golang.org/x/net/context/ctxhttp/cancelreq.go
+++ b/vendor/golang.org/x/net/context/ctxhttp/cancelreq.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build go1.5
+// +build !appengine
 
 package ctxhttp
 
diff --git a/vendor/golang.org/x/net/context/ctxhttp/cancelreq_go14.go b/vendor/golang.org/x/net/context/ctxhttp/cancelreq_go14.go
index 56bcbad..116c07f 100644
--- a/vendor/golang.org/x/net/context/ctxhttp/cancelreq_go14.go
+++ b/vendor/golang.org/x/net/context/ctxhttp/cancelreq_go14.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !go1.5
+// +build appengine
 
 package ctxhttp