Log stack trace when an error occur while deleting event

This will help figuring out root cause of failure to delete event file.

Change-Id: I2f9774c3daf19a04f6b04414ba8145c99bb6e0fe
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java b/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java
index 83aad41..d6ae6b4 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java
@@ -74,7 +74,7 @@
       try {
         Files.delete(refUpdates().resolve(eventKey));
       } catch (IOException e) {
-        logger.atSevere().log("Error while deleting event %s", eventKey);
+        logger.atSevere().withCause(e).log("Error while deleting event %s", eventKey);
       }
     }
   }