Bump Guava to 21.0

Change-Id: Id81705773d191db6a18153d8b2dd4abd2bfd0e60
diff --git a/drivers/default/src/main/java/org/onosproject/driver/query/FullVlanAvailable.java b/drivers/default/src/main/java/org/onosproject/driver/query/FullVlanAvailable.java
index ab9d494..3664077 100644
--- a/drivers/default/src/main/java/org/onosproject/driver/query/FullVlanAvailable.java
+++ b/drivers/default/src/main/java/org/onosproject/driver/query/FullVlanAvailable.java
@@ -20,7 +20,6 @@
 
 import com.google.common.collect.ImmutableSet;
 import org.onlab.packet.VlanId;
-import org.onlab.util.GuavaCollectors;
 import org.onosproject.net.PortNumber;
 import org.onosproject.net.behaviour.VlanQuery;
 import org.onosproject.net.driver.AbstractHandlerBehaviour;
@@ -50,7 +49,7 @@
         return IntStream.range(0, MAX_VLAN_ID)
                 .filter(x -> !EXCLUDED.contains(x))
                 .mapToObj(x -> VlanId.vlanId((short) x))
-                .collect(GuavaCollectors.toImmutableSet());
+                .collect(ImmutableSet.toImmutableSet());
     }
 
 }