Added explicit defining of encoding

At some moment (probably after updating to OS X 10.9) workflow stoped working. Some investigation showed problem with encoding. As @wwwjfy suggested in https://github.com/ddjfreedom/recent-downloads-alfred-v2/issues/12 I've added explicit defining of encoding into recent_downloads.rb and it actually helped.
Merge pull request #16 from smaant/patch-1

Explicit defining of encoding