Update ffmpeg to version 20170918-3ffd3b7
Update ffmpeg to version 20170918-3ffd3b7

Cyianor/scoop,toxeus/scoop,reelsense/scoop,vidarkongsli/scoop,berwyn/scoop,kodybrown/scoop,coonce/scoop,yunspace/scoop,nikolasd/scoop,Congee/scoop,lukesampson/scoop,rasa/scoop