Update to 2018-02-15 release

[benmanns]

Also pushed to my master branch for testing.

$ brew tap benmanns/homebrew-halide
$ brew install halide
$ brew test halide && echo yes
Testing benmanns/halide/halide
==> g++ /usr/local/Cellar/halide/2018.02.15/share/halide/tutorial/lesson_01_basics.cpp -g -I /usr/local/Cellar/halide/2018.02.15/include -L /usr/local/Cellar/halide/2018.02.15/lib -lHalide -o lesson_01 -std=c++11
==> ./lesson_01
yes