Add default values (#1)

Add default values

Reviewed-on: https://gitea.com/gitea/graceful/pulls/1

manager.go

@@ -13,9 +13,9 @@ import (
 )
 
 var (
-	GracefulHammerTime  time.Duration
+	GracefulHammerTime  = 60 * time.Second
 	StartupTimeout      time.Duration
-	GracefulRestartable bool
+	GracefulRestartable = true
 )
 
 type state uint8