use singular form when there's only one diffusion (#1117)

panikweb_templates/templates/episodes/detail.html

@@ -26,7 +26,11 @@
 		{% if episode.subtitle %}
 		<h3 class="episode-subtitle">{{ episode.subtitle }}</h3>
 		{% endif %}
+		{% if diffusions|length > 1 %}
 		<div class="label">Diffusions</div>
+		{% else %}
+		<div class="label">Diffusion</div>
+		{% endif %}
 		<ul class="diffusions custom">
 			{% for schedule in diffusions %}
 				<li><span class="date">{{ schedule.datetime|date:"l d M Y à H:i" }}</span></li>