title: App failing to push to heroku because of gem bundler (Failed to add the host to the list of known hosts (/home/group_home/.ssh/known_hosts))
body: <p>I had encountered this error when attempting to push a spree sandbox cart to test an extension I was going to use. </p>
  
  <p>My Gemfile </p>
  
  <pre><code>gem 'spree_flexi_variants', :git=&gt;'git@github.com:jsqu99/spree_flexi_variants.git', :branch =&gt; 'pre-deface-stable'
  </code></pre>
  
  <p>The output of heroku push:</p>
  
  <pre><code>
  julio@ubuntu:~/rails/sandboxcart $ git push heroku master
  Counting objects: 502, done.
  Delta compression using up to 2 threads.
  Compressing objects: 100% (475/475), done.
  Writing objects: 100% (502/502), 2.63 MiB | 458 KiB/s, done.
  Total 502 (delta 44), reused 0 (delta 0)
  
  -----> Heroku receiving push
  -----> Ruby/Rails app detected
  -----> Detected Rails is not set to serve static_assets
         Installing rails3_serve_static_assets... done
  -----> Configure Rails 3 to disable x-sendfile
         Installing rails3_disable_x_sendfile... done
  -----> Configure Rails to log to stdout
         Installing rails_log_stdout... done
  -----> Gemfile detected, running Bundler version 1.0.7
         Unresolved dependencies detected; Installing...
         Using --without development:test
         Fetching source index for http://rubygems.org/
         Fetching git@github.com:jsqu99/spree_flexi_variants.git
         Failed to add the host to the list of known hosts (/home/group_home/.ssh/known_hosts).
         Permission denied (publickey).
         fatal: The remote end hung up unexpectedly
         An error has occurred in git when running `git clone "git@github.com:jsqu99/spree_flexi_variants.git" "/disk1/tmp/build_1s7xejrz2f9xk/.bundle/gems/ruby/1.9.1/cache/bundler/git/spree_flexi_variants-fc5500c20fdd64421924c0c5673538c7c6822540" --bare --no-hardlinks`. Cannot complete bundling.
         FAILED: http://devcenter.heroku.com/articles/bundler
   !     Heroku push rejected, failed to install gems via Bundler
  
  </code></pre>
  
  <p>The app runs and uses the gem properly but upon trying to deploy that error occurs. I am still in the process of trouble shooting but any help would be appreciated.</p>