[build] Bump log4j2 version to 2.16.0 (#714)

Author: snuyanzin

pom.xml

@@ -81,7 +81,7 @@ under the License.
         <maven.compiler.target>${java.version}</maven.compiler.target>
         <hamcrest.version>1.3</hamcrest.version>
         <slf4j.version>1.7.15</slf4j.version>
-        <log4j.version>2.12.1</log4j.version>
+        <log4j.version>2.16.0</log4j.version>
         <spotless.version>2.4.2</spotless.version>
         <!-- Enforce single fork execution due to heavy mini cluster use in the tests -->
         <flink.forkCount>1</flink.forkCount>