scripts/download.py: use a more terse api for fetching git commit date
The previous api [1] includes in its response patch data among other
things, as such the response size can vary and be big. Use another
api[2] to improve it a bit
[1] Get a single commit, Repositories, https://developer.github.com/v3/repos/commits/#get-a-single-commit
[2] Git Commits, Git Data, https://developer.github.com/v3/git/commits/#get-a-commit
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
(backported from
6e3c2d757a5745dee5cce0b53175b56ad3621d73)