Allow only jp(e)g and png uploads

app/uploaders/picture_uploader.rb

@@ -1,5 +1,3 @@
-# encoding: utf-8
-
 class PictureUploader < CarrierWave::Uploader::Base
 
   # Include RMagick or MiniMagick support:
@@ -38,9 +36,9 @@ class PictureUploader < CarrierWave::Uploader::Base
 
   # Add a white list of extensions which are allowed to be uploaded.
   # For images you might use something like this:
-  # def extension_white_list
-  #   %w(jpg jpeg gif png)
-  # end
+  def extension_white_list
+    %w(jpg jpeg png)
+  end
 
   # Override the filename of the uploaded files:
   # Avoid using model.id or version_name here, see uploader/store.rb for details.