Unify log4j versions and bump from 2.11.0 to 2.13.3

CVE-2020-9488

Closes #66, #67, #74

Change-Id: Ic5447cd7724810d6e143f6be3a676a450a552d96
diff --git a/core/pom.xml b/core/pom.xml
index 32eccd7..8caa289 100644
--- a/core/pom.xml
+++ b/core/pom.xml
@@ -12,6 +12,7 @@
 		<jersey.version>1.19.4</jersey.version>
 		<jetty.version>9.4.19.v20190610</jetty.version>
 		<hibernate.version>5.3.7.Final</hibernate.version>
+		<log4j.version>2.13.3</log4j.version>
 	</properties>
 	<build>
 		<resources>
@@ -184,22 +185,22 @@
 		<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>