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

core/modules/path/migration_templates/d6_url_alias.yml

@@ -1,12 +1,11 @@
 id: d6_url_alias
-label: Drupal 6 URL aliases
+label: URL aliases
 migration_tags:
   - Drupal 6
 source:
   plugin: d6_url_alias
   constants:
     slash: '/'
-
 process:
   source:
     plugin: concat

core/modules/path/migration_templates/d7_url_alias.yml

@@ -0,0 +1,22 @@
+id: d7_url_alias
+label: URL aliases
+migration_tags:
+  - Drupal 7
+source:
+  plugin: d7_url_alias
+  constants:
+    slash: '/'
+process:
+  source:
+    plugin: concat
+    source:
+      - constants/slash
+      - source
+  alias:
+    plugin: concat
+    source:
+      - constants/slash
+      - alias
+  langcode: language
+destination:
+  plugin: url_alias