Assignment Model Missing Attribute For Overrides

[jwong3]

Hi,

Looking at the Canvas API, Assignment seems to be missing the attribute for AssignmentOverride: assignment[assignment_overrides][]

This might be very helpful to add because it seems like we can create the assignment and the override at the same time in one request rather than making two separate requests - creating an assignment before creating the override for it. We can also read in these overrides on an assignment when we request them to be included in the assignment from Canvas.