Bump CarrierWave to 1.3.1
This avoids an extra HEAD request when making request for auth URL (https://github.com/carrierwaveuploader/carrierwave/commit/0b9a64a1bb9f20d1de154dc3bf2e2dd988210220).
Edited by Stan Hu
This avoids an extra HEAD request when making request for auth URL (https://github.com/carrierwaveuploader/carrierwave/commit/0b9a64a1bb9f20d1de154dc3bf2e2dd988210220).