Change gem for Project 2: Using a Third Party API

The `flickr_fu` gem mentioned for Project 2 has not worked with the Flickr API at least since the [Flickr API went SSL-only](http://code.flickr.net/2014/04/30/flickr-api-going-ssl-only-on-june-27th-2014/).  I changed the project to suggest the gem I ended up using--`flickraw`.
Merge pull request #564 from donaldali/patch-39

Change gem for Project 2: Using a Third Party API