fix Hyrax.Schema documentation
fix Hyrax.Schema documentation

this was linking to itself, instead of the class method. this is a big
difference because the class documented here is private, and the `Hyrax.Schema`
method is the appropriate interface devs are going to need to find.

samvera/hyrax,samvera/hyrax,samvera/hyrax,samvera/hyrax