fastgit may be blocked by GFW (see https://t.me/fastgitchannel/81), so
hard-coding its URL is not a good option. Using git URL rewrite feature
is a better choice: https://jdhao.github.io/2021/11/27/git_notes_s4/#use-a-git-mirror-site-for-cloning.
This is a breaking change, since previously I use hub.fastgit.org as the
url, now the url will be default github.com unless the user change it
using the above mentioned method to change the cloning URL.