Add credo to the project and:

- Run mix credo --all to identify possible code optimizations
 - Resolve most of the errors generated by credo such as:
   - Numbers larger than 9999 should be written with underscores: 58_127
   - Modules should have a @moduledoc tag
   - Comparison will always return true

lib/display/notification.ex

@@ -1,4 +1,5 @@
 defmodule Display.Notifications do
+  @moduledoc false
   alias Display.Paint
 
   def congratulate do
@@ -13,8 +14,7 @@ defmodule Display.Notifications do
   defp module_names(modules) do
     modules
     |> Enum.map(&Atom.to_string/1)
-    |> Enum.map(&name/1)
-    |> Enum.join(", ")
+    |> Enum.map_join(", ", &name/1)
     |> Paint.red()
   end