Update CHANGELOG.txt

CHANGELOG.txt

@@ -30,6 +30,7 @@ Changelog
  * Page explorer menu item, search and summary panel are now hidden for users with no page permissions (Tim Heap)
  * Added support for custom date and datetime formats in input fields (Bojan Mihelac)
  * Added support for custom Django REST framework serialiser fields in `Page.api_fields` using a new `APIField` class (Karl Hobley)
+ * Added `classname` argument to `StreamFieldPanel` (Christine Ho).
  * Fix: Marked 'Date from' / 'Date to' strings in wagtailforms for translation (Vorlif)
  * Fix: "File" field label on image edit form is now translated (Stein Strindhaug)
  * Fix: Unreliable preview is now reliable by always opening in a new window (Kjartan Sverrisson)