add "hr"to allowed tags in HTML

because it doesn't hurt and it is useful in event description and all other HTML content

lib/service/formatter/default_scrubbler.ex

@@ -73,6 +73,7 @@ defmodule Mobilizon.Service.Formatter.DefaultScrubbler do
   Meta.allow_tag_with_these_attributes(:h3, [])
   Meta.allow_tag_with_these_attributes(:h4, [])
   Meta.allow_tag_with_these_attributes(:h5, [])
+  Meta.allow_tag_with_these_attributes(:hr, [])
 
   Meta.strip_everything_not_covered()
 end