Don't use parentheses on 0-arity function definitions

lib/mix/tasks/music_library/prod/helpers.ex

@@ -17,7 +17,7 @@ defmodule Mix.Tasks.MusicLibrary.Prod.Helpers do
     end
   end
 
-  defp flyctl_installed?() do
+  defp flyctl_installed? do
     System.find_executable("flyctl")
   end
 end

lib/music_library/application.ex

@@ -37,7 +37,7 @@ defmodule MusicLibrary.Application do
     :ok
   end
 
-  defp skip_migrations?() do
+  defp skip_migrations? do
     # By default, sqlite migrations are run when using a release
     System.get_env("RELEASE_NAME") != nil
   end