Fix missing template import.

biscuit/apps/chronos/templates/chronos/edit_substitution.html

 {# -*- engine:django -*- #}
 
 {% extends "core/base.html" %}
-{% load bootstrap4 i18n %}
+{% load bootstrap4 font_awesome i18n %}
 
 {% block bootstrap4_title %}{% blocktrans %}Edit substitution{% endblocktrans %} - {{ block.super }}{% endblock %}