http2: fix RFC number typo in comment

Fix by Martin Garton in https://golang.org/cl/43370

Change-Id: I5933b136ff667c0f67ec8ebffb52d6f1235232b3
Reviewed-on: https://go-review.googlesource.com/44030
Reviewed-by: Matt Layher <mdlayher@gmail.com>
1 file changed