Fix thumbnail size to 64x64

nova/templates/collection/list.html

@@ -14,9 +14,7 @@
 <div class="row dataset-pad">
   <div class="col-lg-1">
     {% if dataset.has_thumbnail %}
-    <img class="img-responsive" src="{{ url_for("show_dataset",
-    name=collection.user.name, collection_name=collection.name,
-    dataset_name=dataset.name, path='.thumb.jpg') }}"/>
+    <img class="img-responsive" width="64" height="64" src="{{ url_for("show_dataset", name=collection.user.name, collection_name=collection.name, dataset_name=dataset.name, path='.thumb.jpg') }}"/>
     {% else %}
     <img class="img-responsive" src="https://placeholdit.imgix.net/~text?txtsize=33&txt=%C3%97&w=64&h=64"/>
     {% endif %}