Upgrade to Netty 4.1.51.Final

[closes #327]

Author: mp911de

pom.xml

@@ -43,7 +43,7 @@
         <mbr.version>0.2.0.RELEASE</mbr.version>
         <logback.version>1.2.3</logback.version>
         <mockito.version>3.3.3</mockito.version>
-        <netty.version>4.1.50.Final</netty.version>
+        <netty.version>4.1.51.Final</netty.version>
         <postgresql.version>42.2.12</postgresql.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>