``futurize --output-dir`` references undefined logger

Reported by Mark Richardson on the `python-porting` list:

Tried running `futurize` on some of my old python2 code and the futurizer blew up around line 271 with error:

```
NameError: name 'logger' is not defined
```

The original line starts with

```
   logger.info('Output ...
```

and I think it should be

```
   logging.info('Output ...
```
