build: Update version number to 0.3.1

Change-Id: Iebd1ef1cfdc95e9890e8a6017eb77be37aae6c93
Refs: #2588
diff --git a/wscript b/wscript
index 5466d04..af9b841 100644
--- a/wscript
+++ b/wscript
@@ -3,7 +3,7 @@
 from waflib import Logs, Utils, Context
 import os
 
-VERSION = "0.3.0"
+VERSION = "0.3.1"
 APPNAME = "ndn-cxx"
 PACKAGE_BUGREPORT = "http://redmine.named-data.net/projects/ndn-cxx"
 PACKAGE_URL = "http://named-data.net/doc/ndn-cxx/"