shards: ignore fsnotify.ErrEventOverflow

Change-Id: I4c648f539f226be0e286083789d4e4e44376abc3
diff --git a/shards/watcher.go b/shards/watcher.go
index 0407bad..7cc7094 100644
--- a/shards/watcher.go
+++ b/shards/watcher.go
@@ -147,7 +147,9 @@
 				default:
 				}
 			case err := <-watcher.Errors:
-				if err != nil {
+				// Ignore ErrEventOverflow since we rely on the presence of events so
+				// safe to ignore.
+				if err != nil && err != fsnotify.ErrEventOverflow {
 					log.Println("watcher error:", err)
 				}
 			case <-quitter: