Dependency no longer functional

[james-dowling]

This buildpack is meant to be used through heroku-buildpack-multi, but heroku-buildpack-multi is no longer maintained and no longer functions.

When using the buildpack as instructed in the README.md, the following error occurs:

remote: -----> Multipack app detected
remote: WARNING: This buildpack is no longer maintained.
remote:
remote: Please choose a different buildpack or go to https://github.com/ddollar/heroku-buildpack-multi
remote: and fork it to your own account.
remote:
remote: This buildpack will cease to function at the stroke of midnight on January 1, 2017.
remote:  !     Push rejected, failed to compile Multipack app.
remote:
remote:  !     Push failed
remote: Verifying deploy...
remote:
remote: !	Push rejected

Steps to reproduce:

cd /tmp
mkdir -p testing-webp
cd testing-webp

cat <<EOT >> Gemfile
source 'https://rubygems.org'
gem 'rack'
EOT

bundle

cat <<EOT >> .buildpacks
https://github.com/nrj/heroku-buildpack-imagemagick-webp
https://github.com/heroku/heroku-buildpack-nodejs
EOT

cat <<EOT >> config.ru
run lambda { |env| [200, {'Content-Type'=>'text/plain'}, StringIO.new("Hello World!\n")] }
EOT

git init
git add .
git commit -m 'pure rack app'
heroku create
heroku config:set BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi
git push heroku master