warn if minimum-stability is set to non-stable
warn if minimum-stability is set to non-stable

tungbi/heroku-buildpack-nginx-php-phalcon,emeth-/heroku-buildpack-php,CloudSide/heroku-buildpack-php,a2service/heroku-buildpack-php,fgbreel/heroku-buildpack-php,alzheic/heroku-buildpack-aop,pauljfranklin/heroku-buildpack-apache,tungbi/heroku-buildpack-nginx-php-phalcon,tideways/heroku-buildpack-php,tungnguyenson/heroku-buildpack-nginx-php-phalcon,thecsea/heroku-buildpack-php-with-ioncube,commoncurriculum/heroku-buildpack-php,alzheic/heroku-buildpack-aop,wzrdtales/heroku-buildpack-php,jopereyral/heroku-buildpack-php,ActivKonnect/heroku-buildpack-php,rs-makino/buildpack-test,thecsea/heroku-buildpack-php-with-ioncube,createmultimedia/heroku-buildpack-php,0ppy/sample-buildpack,AV4TAr/heroku-buildpack-php,tideways/heroku-buildpack-php,wordpressmonk/herokuphp,rs-makino/buildpack-test,fizz/heroku-buildpack-php,mrapogee/heroku-buildpack-php,dzuelke/heroku-buildpack-php,tucksaun/heroku-buildpack-php,rikur/heroku-buildpack-php,emeth-/heroku-buildpack-php,emeth-/heroku-buildpack-php,pauljfranklin/heroku-buildpack-apache,wzrdtales/heroku-buildpack-php,rs-makino/buildpack-test,philippwiendl/heroku-buildpack-php,flant/heroku-buildpack-php,createmultimedia/heroku-buildpack-php,puteulanus/heroku-buildpack-php,thecsea/heroku-buildpack-php-with-ioncube,bajke992/heroku-buildpack-php,jayelkaake/heroku-buildpack-magento,a2service/heroku-buildpack-php,AV4TAr/heroku-buildpack-php,martijngastkemper/heroku-buildpack-php,ActivKonnect/heroku-buildpack-php,dzuelke/heroku-buildpack-php,CloudSide/heroku-buildpack-php,brendanmcdaniel/heroku-buildpack-php,bartuspan/heroku-buildpack-php,0ppy/sample-buildpack,flant/heroku-buildpack-php,penciu/heroku-php-buildpack,DNESS/heroku-buildpack-php,rikur/heroku-buildpack-php,alzheic/heroku-buildpack-aop,puteulanus/heroku-buildpack-php,emeth-/heroku-buildpack-php,rs-makino/buildpack-test,rikur/heroku-buildpack-php,jayelkaake/heroku-buildpack-magento,martijngastkemper/heroku-buildpack-php,Apelsin/heroku-buildpack-phabricator,flant/heroku-buildpack-php,fgbreel/heroku-buildpack-php,puteulanus/heroku-buildpack-php,mrapogee/heroku-buildpack-php,0ppy/sample-buildpack,heroku/heroku-buildpack-php,rs-makino/buildpack-test,jopereyral/heroku-buildpack-php,wordpressmonk/herokuphp,Apelsin/heroku-buildpack-phabricator,wesrc/heroku-buildpack-php-1,rs-makino/buildpack-test,wesrc/heroku-buildpack-php-1,marcofognog/cedar-14-php-buildpack,dzuelke/heroku-buildpack-php,jayelkaake/heroku-buildpack-magento,tungnguyenson/heroku-buildpack-nginx-php-phalcon,fizz/heroku-buildpack-php,heroku/heroku-buildpack-php,commoncurriculum/heroku-buildpack-php,marcofognog/cedar-14-php-buildpack,penciu/heroku-php-buildpack,heroku/heroku-buildpack-php,a2service/heroku-buildpack-php,tucksaun/heroku-buildpack-php,bartuspan/heroku-buildpack-php,philippwiendl/heroku-buildpack-php,bajke992/heroku-buildpack-php,heroku/heroku-buildpack-php,jopereyral/heroku-buildpack-php,brendanmcdaniel/heroku-buildpack-php,DNESS/heroku-buildpack-php,createmultimedia/heroku-buildpack-php,rikur/heroku-buildpack-php