Fix formatting of changelog entry

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/ChangeLog.d/session-cache-api.txt b/ChangeLog.d/session-cache-api.txt
index e3f25d6..75cc943 100644
--- a/ChangeLog.d/session-cache-api.txt
+++ b/ChangeLog.d/session-cache-api.txt
@@ -1,4 +1,4 @@
-API Changes
+API changes
     * The getter and setter API of the SSL session cache (used for
       session-ID based session resumption) has changed to that of
       a key-value store with keys being session IDs and values