http2: fix a typo
http2: fix a typo

Change-Id: I0c4c58d6488ddf321a5d62b6e9f0dd46f5f40438
Reviewed-on: https://go-review.googlesource.com/33256
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/net