-o, --output flag doesn't create output directory for log file if it doesn't exist already

### Environment
- `interrogate` version(s): 1.5.0
- Python version(s): 3.6-3.9

### Description of the bug
When using the `-o, --output` flag, interrogate doesn't create the parent(s) of the file if they don't already exist:

``` bash
$interrogate -vv -o build/coverage/docstring_coverage.log dir/

FileNotFoundError: [Errno 2] No such file or directory: 'build/coverage/docstring_coverage.log'
```

### What you expected to happen
I would expect that interrogate would create the parent directories that do not exist (e.g. in this case `build/coverage/`.