chore: Bump version to 3.0.0

Author: chaoming0625

brainpy/.python-version

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 
 
-__version__ = "2.6.2"
+__version__ = "3.0.0"
 
 # fundamental supporting modules
 from brainpy import errors, check, tools