Warn more loudly about Leiningen 1.x usage.
Warn more loudly about Leiningen 1.x usage.

heroku/heroku-buildpack-clojure,nvbn/heroku-buildpack-clojure,cedricpineau/heroku-buildpack-clojure-phantomjs,jkutner/heroku-buildpack-lein,heroku/heroku-buildpack-clojure