Change Servlet Spec from 3.0 to 3.1

[hideakikondo]

Problem

Currently our web.xml defines our apps (core/engine) are written in the form of servlet spec 3.0. We use Tomcat 8 in development and testing and recommend users to use it, however according to the following information, tomcat 8 is for servlet spec 3.1.
http://tomcat.apache.org/whichversion.html

This may cause minor issues.

Solution

Change web.xml to use servlet spec 3.1.

[SawamiWataru]

Released v1.6.16