Hey
Hey
Fixes #81
Hi @fieldryand I have found DAG validation bug. ```mermaid graph LR; c-->a; a-->b; b-->a; ``` 
**Describe the bug** timer.After() creates a new timer object each time it is called. Which can cause a memory leak in the for loop. https://github.com/hibiken/asynq/blob/d04888e74845fc7434c6a50755e62ec6ffda5911/subscriber.go#L61-L74 https://github.com/hibiken/asynq/blob/d04888e74845fc7434c6a50755e62ec6ffda5911/syncer.go#L60-L85 **To Reproduce** **Expected behavior**...