[very low priority] doesn't work with spring and Rails 4.2.5

In development environment with spring enabled, either in console or sidekiq worker, 

``` ruby
client = Lowdown::Client.production false, certificate: File.read('/path/to/apple_push_notification.pem')`
```

will get error message "fatal: No live threads left. Deadlock?"
When exiting console, will get message "Couldn't cleanly terminate all actors in 10 seconds!"

it works fine without spring.
