Merge remote-tracking branch 'upstream/release-5.1' into release-5.1-daily-merge-20180706

i18n/en.json

@@ -159,6 +159,10 @@
     "id": "api.channel.delete_channel.deleted.app_error",
     "translation": "The channel has been archived or deleted"
   },
+  {
+    "id": "api.channel.delete_channel.type.invalid",
+    "translation": "Cannot delete direct or group message channels"
+  },
   {
     "id": "api.channel.join_channel.already_deleted.app_error",
     "translation": "Channel is already deleted"