http2/h2demo: add Autocert notification email
http2/h2demo: add Autocert notification email

Add golang-dev as the Autocert notification email so Let's Encrypt can
send us emails. golang-dev is not an ideal choice, but we need something
publicly accessible and there isn't an obvious better option. My
understanding is we should expect essentially no emails so I don't want
to worry too much about it.

Updates golang/go#47108.

Change-Id: Ic3b5b7554d516ea2840bb56499eb3b8f35bf2304
Reviewed-on: https://go-review.googlesource.com/c/net/+/334929
Trust: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
Run-TryBot: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/net