Add timm package to CI (#88)

Summary:
This is required for some models like inception v4

Pull Request resolved: https://github.com/pytorch/executorch/pull/88

Test Plan: After this is merged, we can test OSS with D48524577

Reviewed By: huydhn

Differential Revision: D48568221

Pulled By: kirklandsign

fbshipit-source-id: 09a8d27a99c3a501b84c668c0938a115f4225fb1