Disable nano

I did not know that it was actually enabled on every system. This commit
replaces it with vim.

modules/default.nix

@@ -80,9 +80,11 @@
         git-lfs # not so essential, but required to clone config
         htop
         tmux
-        vim
       ];
 
+      programs.nano.enable = false;
+      programs.vim.defaultEditor = true;
+
       # Clean temporary files on boot
       boot.tmp.cleanOnBoot = true;