enable automatic garbage collection

common/desktop.nix

@@ -78,6 +78,11 @@
   # $ nix search wget
   # allow non-free packages
   nixpkgs.config.allowUnfree = true;
+  nix.gc = {
+    automatic = true;
+    dates = "weekly";
+    options = "--delete-older-than 7d";
+  };
 
   # enable steam
   programs.steam.enable = true;
@@ -105,6 +110,7 @@
     ranger
     rofi
     source-code-pro
+    source-highlight
     terminator
     tree
     vim