Fix new credo warnings

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mix/tasks/mobilizon/instance.ex

@@ -181,7 +181,7 @@ defmodule Mix.Tasks.Mobilizon.Instance do
     else
       shell_error(
         "The task would have overwritten the following files:\n" <>
-          (will_overwrite |> Enum.map(&"- #{&1}\n") |> Enum.join("")) <>
+          Enum.map_join(will_overwrite, "", &"- #{&1}\n") <>
           "Rerun with `-f/--force` to overwrite them."
       )
     end

lib/mix/tasks/mobilizon/users/show.ex

@@ -47,7 +47,7 @@ defmodule Mix.Tasks.Mobilizon.Users.Show do
   defp display_actors(actors) do
     """
     Identities (#{length(actors)}):
-    #{actors |> Enum.map(&display_actor/1) |> Enum.join("")}
+    #{Enum.map_join(actors, &display_actor/1)}
     """
   end