add changes

Author: gongdewei

CHANGES.md

@@ -15,6 +15,7 @@ Release Notes.
 * Bump up apache parent pom to v35.
 * Update Maven to 3.6.3 in mvnw.
 * Fix OOM due to too many span logs.
+* Fix ClassLoader cache OOM issue with WeakHashMap.
 
 All issues and pull requests are [here](https://github.com/apache/skywalking/milestone/242?closed=1)