make the gradebook chunk size always '10'
make the gradebook chunk size always '10'

closes: GRADE-757
ref: GRADE-755

test plan:
 - test plan:
 - Given a course with 1 assignment
 - Given a course with 120 students
 - Given new gradebook enabled
 - When loading the gradebook
 - Then no loading errors are present

Change-Id: Ib934fa96964f4b5af13200d7ea5f080f73df9055
Reviewed-on: https://gerrit.instructure.com/137163
Reviewed-by: Jeremy Neander <20252aad5efdc666f083d82ab63ed0f9f72a043e@instructure.com>
Tested-by: Jenkins
QA-Review: Spencer Olson <7cc0890d6f1f70810a023e7173eca5724d6c8e49@instructure.com>
Product-Review: Keith T. Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>
Reviewed-by: Keith T. Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>

djbender/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms