Bug (typo) in release 0.12.0

```python
soundfile.py:179, in <module>
    177 elif _sys.platform == 'win32':
    178     _explicit_libname = 'libsndfile.dll'
--> 179 elif _sys.plaform == 'linux':
    180     _explicit_libname = 'libsndfile.so'
    181 else:

AttributeError: module 'sys' has no attribute 'plaform'
```

You made mistake in PR #364 