message_edit: Fix weird variable name for edit history events.
message_edit: Fix weird variable name for edit history events.

zulip/zulip,andersk/zulip,zulip/zulip,zulip/zulip,rht/zulip,kou/zulip,rht/zulip,rht/zulip,andersk/zulip,rht/zulip,kou/zulip,kou/zulip,zulip/zulip,andersk/zulip,zulip/zulip,kou/zulip,zulip/zulip,kou/zulip,rht/zulip,andersk/zulip,zulip/zulip,rht/zulip,kou/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip,kou/zulip