v0.6.8

#167 New feature: passing add-in url via dist gulp task using --url parameter
#190 #178 Fix invalid officetheme and other reference to resources
#189 Update default landing page to match dev.office.com design pattern
#186 Dependency update. Fixed badges and documentation.
#187 Fix breaking changes introduced by yeoman generator API update from 0.22 to 0.24
#184 #181 #179 #175 Update manifest elements.