add change description event to timeline

app/modules/user-timeline/user-timeline-item/user-timeline-item-title.service.coffee

@@ -6,7 +6,7 @@ class UserTimelineItemTitle
     _fieldTranslationKey: {
         'status': 'COMMON.FIELDS.STATUS',
         'subject': 'COMMON.FIELDS.SUBJECT',
-        'description': 'COMMON.FIELDS.DESCRIPTION',
+        'description_diff': 'COMMON.FIELDS.DESCRIPTION',
         'points': 'COMMON.FIELDS.POINTS',
         'assigned_to': 'COMMON.FIELDS.ASSIGNED_TO',
         'severity': 'ISSUES.FIELDS.SEVERITY',

app/modules/user-timeline/user-timeline/user-timeline.service.coffee

@@ -8,7 +8,7 @@ class UserTimelineService extends taiga.Service
     _valid_fields: [
         'status',
         'subject',
-        'description',
+        'description_diff',
         'assigned_to',
         'points',
         'severity',