Fix YAML escape bug on Gunicorn log targets

Gunicorn log file targets are not being deserialized correctly by `yaml.load`.  The bug is caused by this behavior:

```python
>>> import yaml
>>> yaml.load("-")
[None]
```

...which results in:

```
registry    54  0.1  0.3  55208 16208 ?        S    19:09   0:00 /usr/bin/python /usr/local/bin/gunicorn --access-logfile [None] --error-logfile [None] --debu
registry    65  0.0  0.8  97604 34064 ?        S    19:09   0:00 /usr/bin/python /usr/local/bin/gunicorn --access-logfile [None] --error-logfile [None] --debu
registry    66  0.0  0.8  97912 34136 ?        S    19:09   0:00 /usr/bin/python /usr/local/bin/gunicorn --access-logfile [None] --error-logfile [None] --debu
registry    75  0.0  0.8  97896 34296 ?        S    19:09   0:00 /usr/bin/python /usr/local/bin/gunicorn --access-logfile [None] --error-logfile [None] --debu
registry    78  0.0  0.8  97776 34124 ?        S    19:09   0:00 /usr/bin/python /usr/local/bin/gunicorn --access-logfile [None] --error-logfile [None] --deb
```

This PR escapes the `-` within double-quotes, which allows it to be deserialized properly.