use selector interpolation from less v1.7
Merge remote-tracking branch 'refs/remotes/origin/master' into upgrade-less
replace the references to app.css.less
Merge pull request #3225 from circleci/upgrade-less

Upgrade less
Merge pull request #3225 from circleci/upgrade-less

Upgrade less
Merge commit '2149bb53547805156f199f8aa53f38b734c9e245'
Merge commit '2f233d54f26b97ec00e76e99d7b1d73964e91272'