Update version in setup.py to reflect v2.3.1 release

Author: drdavella

setup.py

@@ -31,7 +31,7 @@
 builtins._PACKAGE_NAME_ = PACKAGE_NAME
 
 # VERSION should be PEP386 compatible (http://www.python.org/dev/peps/pep-0386)
-VERSION = '2.3.0'
+VERSION = '2.3.1'
 
 # Indicates if this version is a release version
 RELEASE = 'dev' not in VERSION