content/h2push/server: fix pre-Go1.8 build, add copyright header

Change-Id: Iea6d106d2b5a4f987b3f5b69799508bcc876d9c2
Reviewed-on: https://go-review.googlesource.com/39271
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jaana Burcu Dogan <jbd@google.com>
1 file changed