Bump up RRD4j dependency from 2.2 to 3.1

Change-Id: I4bfa18dce4779624205f85c214e0c8f8dcfd1c3a
diff --git a/apps/cpman/app/pom.xml b/apps/cpman/app/pom.xml
index c51978a..76abcdf 100644
--- a/apps/cpman/app/pom.xml
+++ b/apps/cpman/app/pom.xml
@@ -109,7 +109,7 @@
         <dependency>
             <groupId>org.rrd4j</groupId>
             <artifactId>rrd4j</artifactId>
-            <version>2.2</version>
+            <version>3.1</version>
             <scope>provided</scope>
         </dependency>
         <dependency>