treewide: format all files (#57)

Run `nix fmt` at the root of the repository to format all files. I've
done this on my fork and this will help me merge your changes later
without having to deal with un-formatted files.

config/plugins/utils/extra_plugins.nix

@@ -1,4 +1,7 @@
-{pkgs, ...}: {
-  extraPlugins = with pkgs.vimPlugins; [
-  ];
+{ pkgs, ... }:
+{
+  extraPlugins =
+    with pkgs.vimPlugins;
+    [
+    ];
 }