pom.template's ant rules doesn't take variable groupId into account

[cpboyd]

If you use a groupId other than --groupId=com.vaadin.polymer the build will fail due to the Ant rule to clean the directory.

[cpboyd]

Fixed by replacing com/vaadin/polymer with <%= nspath %>

                  <fileset dir="src/main/resources/<%= nspath %>/public/bower_components/" defaultexcludes="no">
                    <include name="**/demo/**/*"/>
                    <include name="**/test/**/*"/>
                    <include name="**/docs/**/*"/>
                    <include name="**/.*"/>
                    <include name="**/index.html"/>
                    <include name="**/package.json"/>
                    <include name="**/*.md"/>
                    <include name="**/*.txt"/>
                  </fileset>
                  <dirset dir="src/main/resources/<%= nspath %>/public/bower_components/">