This updates the bundled http2 package from git rev
5602c733f70afc6dcec6766be0d5034d4c4f14de of the x/net repo for:

  http2: Use NO_ERROR instead of CANCEL when responding before the request is finished
  https://golang.org/cl/40630

  http2: enforce write deadline per stream
  https://golang.org/cl/34727

Updates golang/go#19948
Fixes golang/go#18437

Change-Id: I14500476e91551fa8f27a1aeb8ae3cac9600b74c
Reviewed-on: https://go-review.googlesource.com/41753Reviewed-by: Kale Blankenship <kale@lemnisys.com>
Reviewed-by: Tom Bergan <tombergan@google.com>
Run-TryBot: Kale Blankenship <kale@lemnisys.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>