fix a broken route due to rails 4

refs  CNVS-15128

Test Plan:
* Upload a Picture for a user Avatar
* Should work

Change-Id: If2a78042957871750e0a72e07a5d61974f65df55
Reviewed-on: https://gerrit.instructure.com/42134
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: August Thornton <august@instructure.com>
QA-Review: August Thornton <august@instructure.com>