fix submission api url for pagination
fix submission api url for pagination

fixes CNVS-38266

Test Plan:
- Create a course with multiple sections
- Enroll at least 1 student in each section
- Create an assignment and give each student a grade
- Ensure that your page size is small enough to require multiple requests to get all results
  and then pull submissions via API by section as
 [outlined in the API](https://canvas.instructure.com/doc/api/submissions.html#method.submissions_api.index)
- Notice the urls are correct on every page

Change-Id: I79df6eead31e9ffab0e693ea44e785b51f003eee
Reviewed-on: https://gerrit.instructure.com/126067
Tested-by: Jenkins
QA-Review: Heath Hales <8ca81b68c7e2592ac614bd07f22fcc735ca55f93@instructure.com>
Reviewed-by: Steven Burnett <a0b450117c5d20a22d5c4d52bb8ae13adee003d8@instructure.com>
Product-Review: Steven Burnett <a0b450117c5d20a22d5c4d52bb8ae13adee003d8@instructure.com>
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

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