Fix "process copy" not work in express example

[nlt2390]

The copy propcess will not work because papercut checks and compares file extension:

 copy: (name, path, version, callback)->
   # if using imageId++, 'name' variable does not have file extension 
    if name.indexOf @config.extension isnt -1
      fs.readFile path, 'binary', callback
    else
      callback(new Error("file extension is not #{@config.extension}"))