title: Using ruby and graphviz on heroku with heroku-buildpack-multi
body: <p>I'm trying to deploy my app on heroku. I use declarative_authorization with graphical visualisation. </p>
  
  <p>I installed <code>https://github.com/ddollar/heroku-buildpack-multi</code> <code>heroku config:set BUILDPACK_URL=https://github.com/ddollar/heroku-buildpack-multi</code> and created <code>.buildpacks</code> with:</p>
  
  <pre><code>https://github.com/stigkj/heroku-buildpack-graphviz.git
  https://github.com/heroku/heroku-buildpack-ruby.git
  </code></pre>
  
  <p>Building works fine:</p>
  
  <pre><code>-----&gt; Fetching custom git buildpack... done
  -----&gt; Multipack app detected
  =====&gt; Downloading Buildpack: https://github.com/stigkj/heroku-buildpack-graphviz.git
  =====&gt; Detected Framework: graphviz
  -----&gt; Fetching and installing graphviz
         grapvhiz installed
  =====&gt; Downloading Buildpack: https://github.com/heroku/heroku-buildpack-ruby.git
  =====&gt; Detected Framework: Ruby/Rails
  -----&gt; Using Ruby version: ruby-1.9.3
  </code></pre>
  
  <p>But now I get when I access the graph:</p>
  
  <pre><code>Errno::ENOENT in AuthorizationRulesController#graph
  No such file or directory - dot -q -Tsvg
  </code></pre>
  
  <p>What is the correct path?</p>