Add myself to AUTHORS, update changelog

AUTHORS

@@ -171,3 +171,4 @@ Filippo Valsorda <hi@filippo.io>
 Ivica Ceraj <ceraj@mit.edu>
 Jason Zhu <fmyzjs@gmail.com>
 Marceau Cnudde <marceau.cnudde@gmail.com>
+Braden MacDonald <mail@bradenm.com>

CHANGELOG.rst

@@ -5,6 +5,8 @@ These are notable changes in edx-platform.  This is a rolling list of changes,
 in roughly chronological order, most recent first.  Add your entries at or near
 the top.  Include a label indicating the component affected.
 
+LMS: Do not allow individual due dates to be earlier than the normal due date. LMS-6563
+
 Blades: Course teams can turn off Chinese Caching from Studio. BLD-1207
 
 LMS: Instructors can request and see content of previous bulk emails sent in the instructor dashboard.