Update travis for llvm 3.8
Update travis for llvm 3.8

kgnk/Halide,ronen/Halide,psuriana/Halide,jiawen/Halide,kgnk/Halide,ronen/Halide,ronen/Halide,ronen/Halide,kgnk/Halide,kgnk/Halide,jiawen/Halide,jiawen/Halide,ronen/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,jiawen/Halide,kgnk/Halide,psuriana/Halide,psuriana/Halide,jiawen/Halide,ronen/Halide,jiawen/Halide,ronen/Halide,psuriana/Halide,jiawen/Halide,psuriana/Halide,kgnk/Halide,ronen/Halide,kgnk/Halide