make sure to convert mastodon post IDs to integers

mastodon v2.0.0 changed IDs to be snowflake-like and returns them as
strings in the API

libforget/mastodon.py

@@ -129,7 +129,7 @@ def fetch_acc(acc, cursor=None):
                 post = post_from_api_object(status, acc.mastodon_instance)
                 db.session.merge(post)
                 if 'max_id' not in kwargs:
-                    kwargs['max_id'] = status['id']
+                    kwargs['max_id'] = int(status['id'])
                 kwargs['max_id'] = min(int(kwargs['max_id']), int(status['id']))
 
         else: