fix: Bump version ahead of lateset release (#571)

* fix: Bump version ahead of lateset release

* s/2.2.0a2/2.2.1b0/

Author: c24t

version.py

@@ -4,4 +4,4 @@
 # license that can be found in the LICENSE file or at
 # https://developers.google.com/open-source/licenses/bsd
 
-__version__ = "2.2.0a1"
+__version__ = "2.2.1b0"