Make author avatar optional

_includes/author-profile.html

@@ -4,13 +4,15 @@
 
 <div itemscope itemtype="http://schema.org/Person">
 
-  <div class="author__avatar">
-    {% if author.avatar contains "://" %}
-    	<img src="{{ author.avatar }}" alt="{{ author.name }}">
-    {% else %}
-    	<img src="{{ author.avatar | prepend: "/" | absolute_url }}" class="author__avatar" alt="{{ author.name }}">
-    {% endif %}
-  </div>
+  {% if author.avatar %}
+    <div class="author__avatar">
+      {% if author.avatar contains "://" %}
+      	<img src="{{ author.avatar }}" alt="{{ author.name }}">
+      {% else %}
+      	<img src="{{ author.avatar | prepend: "/" | absolute_url }}" class="author__avatar" alt="{{ author.name }}">
+      {% endif %}
+    </div>
+  {% endif %}
 
   <div class="author__content">
     <h3 class="author__name">{{ author.name }}</h3>