Cannot change version of project facet Dynamic Web Module to 3.0?

Project facets 에서 웹 모듈 버전 변경이 불가하다고 나올때 조치방법

1. web.xml 확인

2. Maven -> Update Project 실행

ref. : 

1. http://stackoverflow.com/questions/18122336/cannot-change-version-of-project-facet-dynamic-web-module-to-3-0

2. http://www.codenuri.com/note/10605?tagTitle=WTP