Upgrade netty 4.1.21

Author: slandelle

pom.xml

@@ -392,7 +392,7 @@
     <surefire.redirectTestOutputToFile>true</surefire.redirectTestOutputToFile>
     <source.property>1.8</source.property>
     <target.property>1.8</target.property>
-    <netty.version>4.1.20.Final</netty.version>
+    <netty.version>4.1.21.Final</netty.version>
     <slf4j.version>1.7.25</slf4j.version>
     <reactive-streams.version>1.0.2</reactive-streams.version>
     <netty-reactive-streams.version>2.0.0</netty-reactive-streams.version>