ZOOKEEPER-4277: update jetty to 9.4.39 due to CVE-2021-28165

Author: Norbert Kalmar <nkalmar@apache.org>

Reviewers: Mohammad Arshad <arshad@apache.org>

Closes #1675 from nkalmar/master

pom.xml

@@ -468,7 +468,7 @@
     <hamcrest.version>2.2</hamcrest.version>
     <commons-cli.version>1.4</commons-cli.version>
     <netty.version>4.1.60.Final</netty.version>
-    <jetty.version>9.4.38.v20210224</jetty.version>
+    <jetty.version>9.4.39.v20210325</jetty.version>
     <jackson.version>2.10.5.1</jackson.version>
     <jline.version>2.14.6</jline.version>
     <snappy.version>1.1.7.7</snappy.version>