swagger UI: handle arrays in Rails format

Arrays in Swagger UI are not being sent in Rails format, i.e. they are not given "[]" suffix. Comma-separated values in Swagger UI should work as arrays.

Test Plan:
- create 2 new courses (let's say with IDs 12 and 13)
- go to Courses / Update Courses in Canvas Live API (swagger UI)
- publish 2 or more courses, e.g.
    account_id: 1
    course_ids: 12, 13
    event: offer
- both courses should now be "published"
- (any other array-type things in the API should also work too)

Fixes SIS-330

Change-Id: I867feaa93a98546426b6a6ff40c11ce56dc43b7a
Reviewed-on: https://gerrit.instructure.com/36575
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Tyler Pickett <tpickett+gerrit@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Eric Adams <eadams@instructure.com>