Use ndash instead of hyphen-minus

Author: hroncok

naucse/templates/course.html

@@ -2,7 +2,7 @@
 
 {% macro session_heading(session, index, plan) %}
     {% if plan|length > 1 %}
-        Lekce {{ index }} -
+        Lekce {{ index }} –
     {% endif %}
     {{ session.title }}
     {% if session.date %}