netty version change

pom.xml

@@ -32,7 +32,7 @@
         <slf4j.version>1.7.7</slf4j.version>
         <groovy.version>2.4.5</groovy.version>
         <snakeyaml.version>1.16</snakeyaml.version>
-        <netty.version>4.1.20.Final</netty.version>
+        <netty.version>4.1.16.Final</netty.version>
         <springframework.version>[4.3.6.RELEASE,5.0.0.M1)</springframework.version>
         <spring-boot.version>[1.5.0.RELEASE,2.0.0.M1)</spring-boot.version>
         <mysql-connector-java.version>5.1.30</mysql-connector-java.version>