Rename Command::cd into Command::current_directory

[GuillaumeGomez]

It's been bothering me for a while so now I finally decided to fix it. :3

cc @syphar

[syphar]

I might be nitpicking, but isn't the better name something around workdir or working-directory? because that's what it is?

In the SandboxBuilder it's called workdir

[GuillaumeGomez]

I'd say no: I'm following the std's Command API naming: https://doc.rust-lang.org/nightly/std/process/struct.Command.html#method.current_dir

Also, it's the current directory where the command will be executed. So I think current_dir is better for this case. And we should also likely update SandboxBuilder's too.

[syphar]

kk, valid