Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/themes/classy/templates/field/field--node--uid.html.twig

@@ -22,7 +22,7 @@
 {%
   set classes = [
     'field',
-    'field--name-' ~ field_name_class,
+    'field--name-' ~ field_name|clean_class,
     'field--type-' ~ field_type|clean_class,
     'field--label-' ~ label_display,
   ]

core/themes/classy/templates/field/field.html.twig

@@ -56,7 +56,7 @@
   {% if multiple %}
     <div{{ attributes.addClass(classes, 'field__items') }}>
       {% for item in items %}
-        <div{{ item.attributes.addClass(classes, 'field__item') }}>{{ item.content }}</div>
+        <div{{ item.attributes.addClass('field__item') }}>{{ item.content }}</div>
       {% endfor %}
     </div>
   {% else %}

core/themes/classy/templates/field/file-link.html.twig

@@ -11,4 +11,5 @@
  * @see template_preprocess_file_link()
  */
 #}
+{{ attach_library('classy/file') }}
 <span{{ attributes }}>{{ icon }} {{ link }}</span>