Use diamond operator

Change-Id: Ief0dabe762acb740476eba5eb033dcfce76426b2
diff --git a/cli/src/main/java/org/onosproject/cli/MetricNameCompleter.java b/cli/src/main/java/org/onosproject/cli/MetricNameCompleter.java
index f05181f..5ab15b0 100644
--- a/cli/src/main/java/org/onosproject/cli/MetricNameCompleter.java
+++ b/cli/src/main/java/org/onosproject/cli/MetricNameCompleter.java
@@ -28,7 +28,7 @@
     @Override
     protected List<String> choices() {
         MetricsService metricsService = AbstractShellCommand.get(MetricsService.class);
-        return new ArrayList<String>(metricsService.getMetrics().keySet());
+        return new ArrayList<>(metricsService.getMetrics().keySet());
     }
 
 }