net/http: update bundled http2
Updates x/net/http2 to git rev
0c607074 for https://golang.org/cl/23311,
"http2: prevent Server from sending status 100 header after anything else"
New test is in the x/net/http2 package (not bundled to std).
Fixes #14030
Change-Id: Ifc6afa4a5fe35977135428f6d0e9f7c164767720
Reviewed-on: https://go-review.googlesource.com/23312
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>