Bump gradle download library
Bump gradle download library

Summary:
https://github.com/michel-kraemer/gradle-download-task#migrating-from-version-3x-to-4x

Major release but we're not affected by any of the changes, could use some of those in CI though.

Reviewed By: jknoxville

Differential Revision: D18394402

fbshipit-source-id: 89773776a11ad0c0d5ff8eb8875eb06546e43072

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper