http2: fix typo in comment

Change-Id: I0febb967cf55118693952332bbb6f740616cfd39
Reviewed-on: https://go-review.googlesource.com/44271
Run-TryBot: David Lazar <lazard@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed