changelog entry for [JENKINS-6604]

changelog.html

@@ -55,6 +55,9 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
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 <ul class=image>
+  <li class=bug>
+    Possible race condition in RemoteClassLoader renders slave unusable.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-6604">issue 6604</a>)
   <li class=bug>
     If the CLI client is aborted during "build -s", abort the build.
   <li class=bug>