rename links to Rasa default branch
@@ -13,7 +13,7 @@ file is managed by ``towncrier``.
You **may** edit previous change logs to fix problems like typo corrections or such.
You can find more information on how to add a new change log entry at
-https://github.com/RasaHQ/rasa/tree/master/changelog/ . -->
+https://github.com/RasaHQ/rasa/tree/main/changelog/ . -->
<!-- TOWNCRIER -->
