Default Parameter#use to :required when undefined

From my understanding of the API Blueprint documentation,
when a parameter is not specified to be required or optional
it is to be considered _required_ by *default*.

Here is where in the documentation I am forming this basis:
https://github.com/apiaryio/api-blueprint/blob/master/API%20Blueprint%20Specification.md#description-11
> * *required* is the _optional_ specifier of a required parameter (this is the *default*)