bump version for v21.0.1dev

Author: mahmoud

setup.py

@@ -11,7 +11,7 @@
 
 
 __author__ = "Mahmoud Hashemi and Glyph Lefkowitz"
-__version__ = "21.0.0"
+__version__ = "21.0.1dev"
 __contact__ = "mahmoud@hatnote.com"
 __url__ = "https://github.com/python-hyper/hyperlink"
 __license__ = "MIT"