Whoa we shouldn't get this frame

Guys, is this right repo to log issues against lumberjack ruby client? Great!

Here's a test case:
1. send normally using client
2. terminate logstash
3. try to write some more data using client
4. get the error:

```
RuntimeError: Whoa we shouldn't get this frame: : /home/lst/lst/vendor/bundle/ruby/2.1.0/gems/jls-lumberjack-0.0.22/lib/lumberjack/client.rb:116:in `ack',
/home/lst/lst/vendor/bundle/ruby/2.1.0/gems/jls-lumberjack-0.0.22/lib/lumberjack/client.rb:109:in `write_hash',
/home/lst/lst/vendor/bundle/ruby/2.1.0/gems/jls-lumberjack-0.0.22/lib/lumberjack/client.rb:44:in `write'
```

Ideas on fixing this are welcome. Ideally, there should be a notification that server is gone and either auto-reconnection code added or just an exception thrown to user that connection is dead.