Doesn't accept signals

I don't think this is a problem with your container, as I'm here after encountering this with the phar in my own container that runs drush, but it appears it won't listen to a signal. 

For example run:

```
docker run -it --rm drush/drush:8 ev "while (true) sleep(5);"
```

.. and try to ctrl+c to kill it. Any ideas?
