Add DefaultCleanUpInterval default.

defaults.go

@@ -1,9 +1,15 @@
 package limiter
 
+import "time"
+
 const (
-	// DefaultPrefix is the prefix to use for the store key.
+	// DefaultPrefix is the default prefix to use for the key in the store.
 	DefaultPrefix = "limiter"
 
-	// DefaultMaxRetry is the maximum number of key retries under race condition.
+	// DefaultMaxRetry is the default maximum number of key retries under
+	// race condition (mainly used with database-based stores).
 	DefaultMaxRetry = 3
+
+	// DefaultCleanUpInterval is the default time duration for cleanup.
+	DefaultCleanUpInterval = 30 * time.Second
 )