Fix typo

Author: asvetlov

setup.py

@@ -46,7 +46,7 @@ def read(f):
     version=version,
     description=("Mixed sync-async queue to interoperate between "
                  "asyncio tasks and classic threads"),
-    long_description='\n\n'.join((read('README.rst'), read('CHANGES.txt'))),
+    long_description='\n\n'.join((read('README.rst'), read('CHANGES.rst'))),
     classifiers=[
         'License :: OSI Approved :: Apache Software License',
         'Intended Audience :: Developers', 'Programming Language :: Python',