This code snippet should contains the prefix "html" like
other examples to be consistent.

Change-Id: I32428452625c016894aebc2011cde2dd614e6ed9
Reviewed-on: https://go-review.googlesource.com/77830Reviewed-by: Gabriel Aszalos <gabriel.aszalos@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Gabriel Aszalos <gabriel.aszalos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>