Explicitly include the default Twilio mediaTypeExtension

[pimterry]

This parameter is marked required, which isn't really correct - it's entirely optional, and defaults to XML.

Unfortunately this parameter must be marked required anyway because it's a path parameter, which is a bit awkward. This change marks that extension as the default, which at least makes clearer imo - it's required that somebody provides this, but the API will do it for you if you don't.

This one is a little debatable. It's a valid spec though, and it is very convenient for my case to be able to say "this param is required and wasn't unspecified, but it's ok because it's defaulted to X anyway"

Actual change looks long, but it's really a single trivial find & replace.

[pimterry]

Hi @MikeRalphson, any thoughts on this one? No urgent hurry, just checking it hasn't been missed.

[MikeRalphson]

Apologies, yes, I forgot about this after seeing the initial notification. Will update the main directory shortly.

[pimterry]

Awesome, thanks!