Fix setup.py

Author: asvetlov

setup.py

@@ -36,7 +36,7 @@ def read(name):
       author_email='[email protected]',
       url='https://github.com/aio-libs/async_timeout/',
       license='Apache 2',
-      py_modules='asyncio_timeout',
+      py_modules=['asyncio_timeout'],
       setup_requires=['pytest-runner'],
       tests_require=['pytest', 'pytest_aiohttp'],
       include_package_data=False)