New upstream release 1.6.1
    
    - https://github.com/less/less.js/blob/v1.6.1/CHANGELOG.md
    - support ^ and ^^ shadow dom selectors
    - fix sourcemap selector (used to report end of the element or selector) and
      directive position (previously not supported)
    - fix parsing empty less files
    - error on (currently) ambiguous guards on multiple css selectors
    - older environments - protect against typeof regex returning function
    - Do not use default keyword
    - use innerHTML in tests, not innerText
    - protect for-in in case Array and Object prototypes have custom fields