Search: requests for learner avatars are returning 403

[pdpinch]

Steps to Reproduce

1. Login as a user with the staff role in DEDP on prod
2. go to https://micromasters.herokuapp.com/learners/

Expected behavior

You will see personalized avatars for users who have uploaded them, like Anna.

Actual behavior

Requests to S3 for the avatars returns a 403 error

[pdpinch]

wrong repo