AssociatedMaterial in ReferencedMaterial.md wrongly specified "ocx" instead of oerschema as source

[science]

I think "ocx:AssociatedMaterial" should be http://oerschema.org/AssociatedMaterial

on page: https://github.com/K12OCX/k12ocx-specs/blob/master/inpage/referencedmaterial.md

as this is not an "ocx" invention, but a relied upon property from oerschema..

[science]

@philbarker & @rsaksida - do you agree? If so, I'll make this change.. (I'll change it all in all the yaml files too).

[philbarker]

@science yes, I think you should.

To get the history right, it is an OCX invention that was adopted by OERSchema (see their issue #32). There is also http://oerschema.org/SupplementalMaterial/ for ocx:SupplementalMaterial and http://oerschema.org/ReferencedMaterial/ for ocx:ReferencedMaterial

[rsaksida]

@science you're right! I think I missed it in the OER schema.