grunt-modernizr: Fatal error: Generate is not a function

This issue only started a day ago, when running grunt-modernizr im getting Fatal error: Generate is not a function at the Building your customized Modernizr stage. Looks like Modernizr is failing to build - https://travis-ci.org/Modernizr/Modernizr

This is on a clean install of grunt-modernizr and therefor Modernizr too, i can take a previous install and it works.

any help would be appreciated.

Screenshot of the error.