feat(nix): set dock orientation to left

Signed-off-by: Seongmin Lee <[e-mail]>

nix/darwin.nix

···
     autohide-time-modifier = 0.6;
     mru-spaces = false;
     show-recents = false;
+    orientation = "left";
     # Disable bottom-right corner action
     wvous-br-corner = 1;
     # persistent-apps = [];