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

core/profiles/standard/config/install/rdf.mapping.node.article.yml

@@ -1,3 +1,10 @@
+langcode: en
+status: true
+dependencies:
+  config:
+    - node.type.article
+  module:
+    - node
 id: node.article
 targetEntityType: node
 bundle: article
@@ -26,22 +33,17 @@ fieldMappings:
   comment:
     properties:
       - 'schema:comment'
-    mapping_type: 'rel'
+    mapping_type: rel
   comment_count:
     properties:
       - 'schema:interactionCount'
     datatype_callback:
       callable: 'Drupal\rdf\SchemaOrgDataConverter::interactionCount'
       arguments:
-        interaction_type: 'UserComments'
+        interaction_type: UserComments
   field_image:
     properties:
       - 'schema:image'
   field_tags:
     properties:
       - 'schema:about'
-dependencies:
-  config:
-    - node.type.article
-  module:
-    - node