title: Heroku push failing due to New Relic RPM gem
body: <p>I've got <code>gem 'newrelic_rpm'</code> in my Gemfile as per Heroku's <a href="https://devcenter.heroku.com/articles/newrelic#addon_installation" rel="nofollow noreferrer">documentation</a>. When I attempt to run <code>git push heroku master</code> I receive the following:</p>
  
  <pre><code>-----&gt; Ruby/Rails app detected
  -----&gt; Installing dependencies using Bundler version 1.3.0.pre.5
         Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin --deployment
         Fetching gem metadata from https://rubygems.org/........
         Fetching gem metadata from https://rubygems.org/..
         Could not find newrelic_rpm-3.5.6.46 in any of the sources
   !
   !     Failed to install gems via Bundler.
   !
   !     Heroku push rejected, failed to compile Ruby/rails app
  
  To git@heroku.com:reponame.git
   ! [remote rejected] master -&gt; master (pre-receive hook declined)
  </code></pre>
  
  <p>Any ideas on how to fix this? I've already tried <code>bundle update</code> as per this SO answer: <a href="https://stackoverflow.com/a/4576816/337903">https://stackoverflow.com/a/4576816/337903</a> to no avail.</p>