Upgrade fog-aws to v3.7.0

This adds multi-threaded support for copying files and fixes some an
issue with AssumeRoleWithWebIdentity that may resolve an issue with AWS
EKS.

CHANGELOG:
https://github.com/fog/fog-aws/blob/master/CHANGELOG.md

Diff: https://github.com/fog/fog-aws/compare/v3.6.7..v3.7.0