Pass through the allowHttp1 option for fallback HTTP/2 to HTTP/1

[jasonmobley]

In the spot where createSecureServer is called, can it include the allowHttp1 option so that a "http2" protocol server still functions for clients that don't load with HTTP/2?

Without this, a misbehaving client gets a response like:

Missing 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.

Relevant NodeJS docs: https://nodejs.org/api/http2.html#http2createsecureserveroptions-onrequesthandler

edit: this is specifically in versions >=5.0.0 where the http2 stuff was recently updated