Handle sensitive property.

test/fixtures/mastodon-post-activity.json

@@ -36,7 +36,7 @@
         "inReplyTo": null,
         "inReplyToAtomUri": null,
         "published": "2018-02-12T14:08:20Z",
-        "sensitive": false,
+        "sensitive": true,
         "summary": "cw",
         "tag": [
             {

test/web/activity_pub/transmogrifier_test.exs

@@ -33,6 +33,7 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       ]
       assert object["actor"] == "http://mastodon.example.org/users/admin"
       assert object["attributedTo"] == "http://mastodon.example.org/users/admin"
+      assert object["sensitive"] == true
     end
 
     test "it works for incoming follow requests" do