Bump earmark from 1.3.6 to 1.4.0

Bumps [earmark](https://github.com/pragdave/earmark) from 1.3.6 to 1.4.0.
- [Release notes](https://github.com/pragdave/earmark/releases)
- [Changelog](https://github.com/pragdave/earmark/blob/master/RELEASE.md)
- [Commits](https://github.com/pragdave/earmark/compare/v1.3.6...v1.4.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

mix.exs

@@ -87,7 +87,7 @@ defmodule Mobilizon.Mixfile do
       {:plug_cowboy, "~> 2.0"},
       {:atomex, "0.3.0"},
       {:cachex, "~> 3.1"},
-      {:earmark, "~> 1.3.1"},
+      {:earmark, "~> 1.4.0"},
       {:geohax, "~> 0.3.0"},
       {:mogrify, "~> 0.7.2"},
       {:premailex, "~> 0.3.0"},