Reduce default retries to 20 days

This equates to roughly 1 week of retrying.
Merge branch 'master' of github.com:8tracks/sidekiq
Digestible worker changes

* By default all DigestibleWorker classes will have their pending keys
  expire. Fixes issues where sidekiq crashes kept pending keys or
  working keys on the server.

* After the last retry, DigestibleWorker classes will have their working
  key removed (to speed up removal of key rather than wait for TTL)