Bump version to v0.4.21

Author: 1st1

setup.py

@@ -96,7 +96,7 @@ def build_extensions(self):
     author='Yury Selivanov',
     author_email='[email protected]',
     platforms=['*nix'],
-    version='0.4.20',
+    version='0.4.21',
     packages=['uvloop'],
     cmdclass={'build_ext': libuv_build_ext},
     ext_modules=[