Speed installation: change git clone 

Change `git clone url` to `git clone url --depth=1`

https://git-scm.com/docs/git-clone

> --depth <depth>
> Create a shallow clone with a history truncated to the specified number of commits. Implies --single-branch unless --no-single-branch is given to fetch the histories near the tips of all branches. If you want to clone submodules shallowly, also pass --shallow-submodules.
