Update llvm versions for travis
Update llvm versions for travis


Former-commit-id: 6fd9e899e05fa21664aabde5899465b7d2686086
Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide