fix deprecation warning

Author: kroepke

src/main/java/org/graylog/plugins/usagestatistics/util/MetricUtils.java

@@ -27,7 +27,7 @@
 import java.util.concurrent.Callable;
 import java.util.concurrent.TimeUnit;
 
-import static com.google.common.base.Objects.firstNonNull;
+import static com.google.common.base.MoreObjects.firstNonNull;
 
 public class MetricUtils {
     private static final Counter EMPTY_COUNTER = new Counter() {