Fix jekyll build warning

courses/meta/former.html

@@ -7,7 +7,7 @@ permalink: /courses/former/
 {% assign courses = site.pages | where: "layout", "course" | sort: "title" %}
 {% assign semesters = site.semesters.former | reverse %}
 {% for semester in semesters %}
-    {% assign offers = (courses | where_exp: "c", "c.semesters contains semester") %}
+    {% assign offers = courses | where_exp: "c", "c.semesters contains semester" %}
     
     {% if offers.size > 0%}