CHANGELOG: Document HTML syntax fix

Documenting:
4aa7f1d Fixed syntactical error when generating HTML mails

The commit by Dennis Keitzel fixed a typo in the HTML which dated back
to 00e2eecc (Spread cmd_run() logic out into Feed methods,
2012-10-04).

Signed-off-by: W. Trevor King <wking@tremily.us>