Update Travis to support SDL 2.0.2 and ffmpeg 2.1.4 

Changelogs:

http://forums.libsdl.org/viewtopic.php?t=10088
http://git.videolan.org/?p=ffmpeg.git;a=shortlog;h=n2.1.4

And why do we use Lua 5.1.4 as 5.1.5 is the newest version in the 5.1 branch?