Upgrade to Log4J 2.11

Author: jhoeller

build.gradle

@@ -51,7 +51,7 @@ configure(allprojects) { project ->
 	ext.junitPlatformVersion = "1.0.3"
 	ext.junitVintageVersion  = "4.12.3"
 	ext.kotlinVersion        = "1.2.30"
-	ext.log4jVersion         = "2.10.0"
+	ext.log4jVersion         = "2.11.0"
 	ext.nettyVersion         = "4.1.22.Final"
 	ext.reactorVersion       = "Bismuth-SR7"
 	ext.rxjavaVersion        = "1.3.6"