Add support for Big Sur

[Halo-Michael]

Now Big Sur (macOS 11.0) mounted a snapshot on rootfs, just same as iOS11.3. So I updated snappy for collect system snapshot name on Big Sur.
Since it has not been updated for iOS, I did not change the version number.

[sbingner]

Can I get you to update this to not change whitespace?

[Halo-Michael]

Yes.
The reason for my modification is that the format of your original code is confusing, sometimes using four-byte spaces as indentation, and sometimes using \t as indentation. I want to unify the code style to improve the viewing. Since your code generally uses \t as indentation, I replaced the four-byte space with \t.

[Halo-Michael]

I think it's because you coding between vim and Xcode. Xcode will switch \t with four-byte space.