Bump version to 2.1.0.b2

Author: kozo2

setup.py

@@ -106,7 +106,7 @@ def run(self):
 
 setup(
     name='ecell4_base',
-    version = '2.1.0b1',
+    version = '2.1.0b2',
     license = "the GNU General Public License v2",
     author = "Kazunari Kaizu",
     author_email = "kaizu@riken.jp",