Test coverage: Switch to covertool to get cobertura output

This allows to have coverage information integrated into Gitlab

mix.exs

@@ -13,8 +13,7 @@ defmodule Pleroma.Mixfile do
       start_permanent: Mix.env() == :prod,
       aliases: aliases(),
       deps: deps(),
-      test_coverage: [tool: ExCoveralls],
-      preferred_cli_env: ["coveralls.html": :test],
+      test_coverage: [tool: :covertool, summary: true],
       # Docs
       name: "Pleroma",
       homepage_url: "https://pleroma.social/",
@@ -207,8 +206,7 @@ defmodule Pleroma.Mixfile do
       {:ex_machina, "~> 2.4", only: :test},
       {:credo, "~> 1.4", only: [:dev, :test], runtime: false},
       {:mock, "~> 0.3.5", only: :test},
-      # temporary downgrade for excoveralls, hackney until hackney max_connections bug will be fixed
-      {:excoveralls, "0.12.3", only: :test},
+      {:covertool, "~> 2.0", only: :test},
       {:hackney, "~> 1.18.0", override: true},
       {:mox, "~> 1.0", only: :test},
       {:websocket_client, git: "https://github.com/jeremyong/websocket_client.git", only: :test}