Update example to allow downgrading to http1

[avimar]

Issues

When following the example, many connections don't work. e.g. curl returned:

Unknown ALPN Protocol, expected h2 to be available. If this is a HTTP request: The server was not configured with the allowHTTP1 option or a listener for the unknownProtocol event.

What does this PR do?

Allows automatic downgrade to http1. Node's http2 module allows https or http2 with the same code.

[stale[bot]]

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