Bump log4j.version from 2.6.2 to 2.14.0

Bumps `log4j.version` from 2.6.2 to 2.14.0.

Updates `log4j-slf4j-impl` from 2.6.2 to 2.14.0

Updates `log4j-core` from 2.6.2 to 2.14.0

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

pom.xml

@@ -55,7 +55,7 @@
     <properties>
         <wicket.version>7.8.0</wicket.version>
         <jetty9.version>9.2.19.v20160908</jetty9.version>
-        <log4j.version>2.6.2</log4j.version>
+        <log4j.version>2.14.0</log4j.version>
         <junit.version>4.12</junit.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <!-- allowed values: R7, 1.0, 1.5, 2.0 or none -->