Upgrade to Netty 4.1.21

build.gradle

@@ -52,12 +52,12 @@ configure(allprojects) { project ->
 	ext.junitVintageVersion  = "4.12.3"
 	ext.kotlinVersion        = "1.2.21"
 	ext.log4jVersion         = "2.10.0"
-	ext.nettyVersion         = "4.1.20.Final"
+	ext.nettyVersion         = "4.1.21.Final"
 	ext.reactorVersion       = "Bismuth-SR5"
 	ext.rxjavaVersion        = "1.3.5"
 	ext.rxjavaAdapterVersion = "1.2.1"
 	ext.rxjava2Version       = "2.1.9"
-	ext.slf4jVersion         = "1.7.25"	// spring-jcl + consistent 3rd party deps
+	ext.slf4jVersion         = "1.7.25"	 // spring-jcl + consistent 3rd party deps
 	ext.tiles3Version        = "3.0.8"
 	ext.tomcatVersion        = "8.5.27"
 	ext.undertowVersion      = "1.4.22.Final"