Unify log4j versions and bump from 2.11.0 to 2.13.3

CVE-2020-9488

Closes #71

Change-Id: I4a6c9bdac66320a10b7eca47dff2ace23633bf1d
diff --git a/pom.xml b/pom.xml
index 04f8b94..43c2152 100644
--- a/pom.xml
+++ b/pom.xml
@@ -38,6 +38,7 @@
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>		
 		<jackson.version>[2.9.5,)</jackson.version>
 		<java.version>1.8</java.version>
+		<log4j.version>2.13.3</log4j.version>
 	</properties>
 	
 	<repositories>
@@ -110,22 +111,22 @@
 		<dependency>
 			<groupId>org.apache.logging.log4j</groupId>
 			<artifactId>log4j-api</artifactId>
-			<version>2.11.0</version>
+			<version>${log4j.version}</version>
 		</dependency>
 		<dependency>
 			<groupId>org.apache.logging.log4j</groupId>
 			<artifactId>log4j-core</artifactId>
-			<version>2.11.0</version>
+			<version>${log4j.version}</version>
 		</dependency>
 		<dependency>
 			<groupId>org.apache.logging.log4j</groupId>
 			<artifactId>log4j-slf4j-impl</artifactId>
-			<version>2.11.0</version>
+			<version>${log4j.version}</version>
 		</dependency>
 		<dependency>
 			<groupId>org.apache.logging.log4j</groupId>
 			<artifactId>log4j-jul</artifactId>
-			<version>2.11.0</version>
+			<version>${log4j.version}</version>
 			<exclusions>
 				<exclusion>
 					<groupId>org.slf4j</groupId>