fix: relative dir installables

A leftover `current_dir` in the command builder for installables
resulted in `nix-weather ./#` invocations, and others relying on
relative filesystem paths failing.

Resolves: #20
Signed-off-by: Christina Sørensen <christina@cafkafk.com>

crates/nix-weather/src/nix.rs

@@ -33,7 +33,6 @@ fn get_installable_drv_path(
   installable: &str,
 ) -> std::io::Result<std::process::Output> {
   Command::new("nix")
-    .current_dir(Path::new(config_dir))
     .args(["build", "--quiet", installable, "--dry-run", "--json"])
     .output()
 }