fix #44

[VuiMuich]

fixes #44

The lib update of the nix package to 0.25 brought removed the argument in the gethostname function.

This lead to:

error[E0061]: this function takes 0 arguments but 1 argument was supplied
    --> .../.cargo/registry/src/github.com-1ecc6299db9ec823/nsh-0.4.2/src/prompt.rs:131:25
     |
131  |     let hostname_cstr = unistd::gethostname(&mut hostname_buf).expect("failed to get hostname");
     |                         ^^^^^^^^^^^^^^^^^^^ ----------------- argument unexpected
     |
note: function defined here
    --> .../.cargo/registry/src/github.com-1ecc6299db9ec823/nix-0.25.0/src/unistd.rs:1020:8
     |
1020 | pub fn gethostname() -> Result<OsString> {
     |        ^^^^^^^^^^^
help: remove the extra argument
     |
131  |     let hostname_cstr = unistd::gethostname().expect("failed to get hostname");
     |                         ~~~~~~~~~~~~~~~~~~~~~

For more information about this error, try `rustc --explain E0061`.
error: could not compile `nsh` due to previous error
error: failed to compile `nsh v0.4.2`, intermediate artifacts can be found at `/var/folders/dt/97jrrt3s3yn7z7bgr3rv0wy40000gn/T/cargo-installHlVCo7`

[nuta]

Wow! Thanks a lot!

[VuiMuich]

Thank you for merging and keep up the good work!