Use Buffer.from #26

https://github.com/azu/githon/blob/3de1998203e58cad4c646a678d11cb47645ffbbc/packages/githon/lib/fs/mock.js#L51

supress deprecated warning

(node:37612) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.