Format nix language files

lua/formatterconfiguration.lua

@@ -43,6 +43,14 @@ require("formatter").setup({
 			require("formatter.filetypes.rust").rustfmt,
 		},
 
+		nix = {
+			function()
+				return {
+					exe = "nixfmt",
+				}
+			end,
+		},
+
 		haskell = {
 			function()
 				-- Full specification of configurations is down below and in Vim help