increment version

Author: jiaaro

setup.py

@@ -8,7 +8,7 @@
 
 setup(
     name='pydub',
-    version='0.20.0',
+    version='0.21.0',
     author='James Robert',
     author_email='jiaaro@gmail.com',
     description='Manipulate audio with an simple and easy high level interface',