Remove use of Guava's deprecated toStringHelper

Change-Id: I264afc337a9f325a23f988a6349a74451910e7d0

@@ -15,7 +15,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
-import static com.google.common.base.Objects.toStringHelper;
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Produces a package & source catalogue.

@@ -2,7 +2,7 @@ package org.onlab.jdvue;
 
 import java.util.Objects;
 
-import static com.google.common.base.Objects.toStringHelper;
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Abstraction of a dependency segment.

@@ -5,7 +5,7 @@ import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 
-import static com.google.common.base.Objects.toStringHelper;
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Simple representation of a Java package dependency cycle.

@@ -4,7 +4,7 @@ import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 
-import static com.google.common.base.Objects.toStringHelper;
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Simple abstraction of a Java package for the purpose of tracking

@@ -2,7 +2,7 @@ package org.onlab.jdvue;
 
 import java.util.*;
 
-import static com.google.common.base.Objects.toStringHelper;
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Simple abstraction of a Java source file for the purpose of tracking