title: Rails 4: KeyError (:access_token_secret credential is nil): using paperclip dropbox gem
body: <p>Trying to upload files using the paperclip-dropbox gem. Works in localhost
  but when i try on heroku i get error KeyError <strong>(:access_token_secret credential is nil):</strong></p>
  
  <pre><code> KeyError (:access_token_secret credential is nil):
  2014-04-29T20:27:00.982579+00:00 app[web.1]: Started POST "/listings" for 92.5.114.214 at 2014-04-29 20:27:00 +0000
  2014-04-29T20:27:00.991481+00:00 app[web.1]: Completed 500 Internal Server Error in 3ms
  2014-04-29T20:27:00.982590+00:00 app[web.1]: Started POST "/listings" for 92.5.114.214 at 2014-04-29 20:27:00 +0000
  2014-04-29T20:27:00.987444+00:00 app[web.1]: Processing by ListingsController#create as HTML
  2014-04-29T20:27:00.992963+00:00 app[web.1]: 
  2014-04-29T20:27:00.992964+00:00 app[web.1]: **KeyError (:access_token_secret credential is nil):**
  2014-04-29T20:27:00.992968+00:00 app[web.1]: 
  2014-04-29T20:27:00.992956+00:00 app[web.1]:   app/controllers/listings_controller.rb:27:in `create'
  2014-04-29T20:27:00.988120+00:00 app[web.1]:   Parameters: {"utf8"=&gt;"✓", "authenticity_token"=&gt;"I7v0J20Qv8IX7bl47AOssqFvv7xaO+X/JqJ1YGZF0Ig=", "listing"=&gt;{"name"=&gt;"test", "description"=&gt;"test", "price"=&gt;"12", "image"=&gt;#&lt;ActionDispatch::Http::UploadedFile:0x007f502b6ed980 @tempfile=#&lt;Tempfile:/tmp/RackMultipart20140429-2-1u8n0ay&gt;, @original_filename="applemac.jpg", @content_type="image/jpeg", @headers="Content-Disposition: form-data; name=\"listing[image]
  "; filename=\"applemac.jpg\"\r\nContent-Type: image/jpeg\r\n"&gt;}, "commit"=&gt;"Create Listing"}
  </code></pre>
  
  <p>heroku config shows </p>
  
  <pre><code>ACCESS_TOKEN_SECRET:        m7r66o1it3xxxxx
  APP_SECRET:                 incev12hukxxxxx
  DATABASE_URL:               postgres://fklmdpqvdabc:5MPF_gpvHqsxqi55g5kQEEpttD@ec2-54-83-201-54.compute-1.amazonaws.com:5432/ddsldn4k8ve16o
  HEROKU_POSTGRESQL_TEAL_URL: postgres://fklmdpqvdabc:5MPF_gpvHqsxqi55g5kQEEpttD@ec2-54-83-201-54.compute-1.amazonaws.com:5432/ddsldn4k8ve16o
  LANG:                       en_US.UTF-8
  RACK_ENV:                   production
  RAILS_ENV:                  production
  </code></pre>
  
  <p>and the application.yml </p>
  
  <pre><code>APP_SECRET: "incev12huxxxxxx"
  ACCESS_TOKEN_SECRET: "m7r66o1xxxxxxx
  </code></pre>
  
  <p>dropbox folder </p>
  
  <pre><code>app_key: "3b0nq7axxxxxxxx"
  app_secret: &lt;%= ENV["APP_SECRET"] %&gt;
  access_token: "v30cwshpxxxxxxx"
  access_token_secret: &lt;%= ENV["APP_TOKEN_SECRET"] %&gt;
  user_id: "3xxxxxx"
  access_type: "app_folder""
  </code></pre>