update to Guava 20
diff --git a/java/pom.xml b/java/pom.xml
index bc71fdc..e8008f4 100644
--- a/java/pom.xml
+++ b/java/pom.xml
@@ -82,7 +82,7 @@
       <dependency>
         <groupId>com.google.guava</groupId>
         <artifactId>guava</artifactId>
-        <version>19.0</version>
+        <version>20.0</version>
       </dependency>
     </dependencies>
   </dependencyManagement>