Updating Guava dependency version (#734)

* Updated pom.xml to reflect Loxigen version update.

* Updating Guava version to keep in step with Loxigen.

pom.xml

@@ -143,7 +143,7 @@
 		<dependency>
 			<groupId>com.google.guava</groupId>
 			<artifactId>guava</artifactId>
-			<version>13.0.1</version>
+			<version>20.0</version>
 		</dependency>
 		<dependency>
 			<groupId>ch.qos.logback</groupId>