Avoid 0 duration GC event times (#1170)

We noticed `:dist-avg` under 1ms for ZGC and `getDuration` is in milliseconds, so
we must be regularly seeing events that start and end in the same millisecond.

spectator-ext-gc/src/main/java/com/netflix/spectator/gc/GcLogger.java

@@ -252,7 +252,8 @@ private void processGcEvent(GarbageCollectionNotificationInfo info) {
       .withTag("action", info.getGcAction())
       .withTag("cause", info.getGcCause());
     Timer timer = Spectator.globalRegistry().timer(eventId);
-    timer.record(info.getGcInfo().getDuration(), TimeUnit.MILLISECONDS);
+    long duration = Math.max(1, info.getGcInfo().getDuration());
+    timer.record(duration, TimeUnit.MILLISECONDS);
 
     // Update promotion and allocation counters
     updateMetrics(info.getGcName(), info.getGcInfo());