Fix typo

Co-authored-by: Eksperimental <eksperimental@autistici.org>

Author: Papipo

lib/mix/lib/mix/tasks/compile.app.ex

@@ -271,7 +271,7 @@ defmodule Mix.Tasks.Compile.App do
   defp merge_project_application(best_guess, _project, application) do
     if not Keyword.keyword?(application) do
       Mix.raise(
-        "Application configuration passed as :application should be a keyword list, , got: #{inspect(application)}"
+        "Application configuration passed as :application should be a keyword list, got: #{inspect(application)}"
       )
     end