title: Heroku run rake db:migrate error with "no such file to load -- bundler/setup"
body: <p>I'm trying to do a "heroku run rake db:migrate", and get this error:</p>
  
  <pre><code>es-MacBook-Pro:project e$ heroku run rake db:migrate
  Running rake db:migrate attached to terminal... up, run.1
  (in /app)
  rake aborted!
  no such file to load -- bundler/setup
  &lt;internal:lib/rubygems/custom_require&gt;:29:in `require'
  &lt;internal:lib/rubygems/custom_require&gt;:29:in `require'
  /app/config/boot.rb:6:in `&lt;top (required)&gt;'
  &lt;internal:lib/rubygems/custom_require&gt;:29:in `require'
  &lt;internal:lib/rubygems/custom_require&gt;:29:in `require'
  /app/config/application.rb:1:in `&lt;top (required)&gt;'
  &lt;internal:lib/rubygems/custom_require&gt;:29:in `require'
  &lt;internal:lib/rubygems/custom_require&gt;:29:in `require'
  /app/Rakefile:5:in `&lt;top (required)&gt;'
  /usr/local/lib/ruby/1.9.1/rake.rb:2373:in `load'
  /usr/local/lib/ruby/1.9.1/rake.rb:2373:in `raw_load_rakefile'
  /usr/local/lib/ruby/1.9.1/rake.rb:2007:in `block in load_rakefile'
  /usr/local/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
  /usr/local/lib/ruby/1.9.1/rake.rb:2006:in `load_rakefile'
  /usr/local/lib/ruby/1.9.1/rake.rb:1991:in `run'
  /usr/local/bin/rake:31:in `&lt;main&gt;'
  </code></pre>
  
  <p>I have no idea how to interpret this error. Does anyone have any clue?</p>