Fix manual json for mastodon outbox

david/mastodon/outbox_content.json

         {
             "actor": "https://larlet.fr/david/",
             "cc": [
-                "https://www.w3.org/ns/activitystreams#Public",
+                "https://www.w3.org/ns/activitystreams#Public"
             ],
             "id": "https://larlet.fr/david/2020/04/10/",
             "object": {
                 "attachment": [],
                 "attributedTo": "https://larlet.fr/david/",
                 "cc": [
-                    "https://www.w3.org/ns/activitystreams#Public",
+                    "https://www.w3.org/ns/activitystreams#Public"
                 ],
                 "content": "<p><a href=\"https://larlet.fr/david/2020/04/10/\">Résistance</a> by <span class=\"h-card\"><a href=\"https://mastodon.social/@dav\" class=\"u-url mention\">@<span>dav</span></a></span></p>",
                 "conversation": "tag:larlet.fr/david/2020/04/10/",