Mark some of the nifty-examples deps as test-scoped only
Mark some of the nifty-examples deps as test-scoped only

This fixes some dependency checker errors which should up in incremental rebuilds of nifty, but don't show up in clean builds.

javazhangtao/nifty,buzzxu/nifty,electrum/nifty,andrewcox/nifty,alandau/nifty,facebook/nifty,szulijun/nifty,ivmaykov/nifty