update 1.21 changelog

Signed-off-by: Andy Green <andy.green@linaro.org>
diff --git a/changelog b/changelog
index e801e51..fc866de 100644
--- a/changelog
+++ b/changelog
@@ -1,6 +1,13 @@
 Changelog
 ---------
 
+v1.21-chrome26-firefox18
+========================
+
+ - Fixes buffer overflow bug in max frame size handling if you used the
+ 	default protocol buffer size.  If you declared rx_buffer_size in your
+	protocol, which is recommended anyway, your code was unaffected.
+
 v1.2-chrome26-firefox18
 =======================