disable AVX512 for Skylake processors to fix travis

.travis.yml

@@ -60,7 +60,7 @@ script:
 # Tutorials and tests
 - mkdir build
 - cd build
-- cmake -DCMAKE_BUILD_TYPE=$CONFIG -DLIBIGL_BUILD_TESTS=ON -DLIBIGL_BUILD_TUTORIALS=ON ../
+- cmake -DCMAKE_BUILD_TYPE=$CONFIG -DLIBIGL_BUILD_TESTS=ON -DLIBIGL_BUILD_TUTORIALS=ON -DEMBREE_ISA_AVX512SKX=OFF ../
 - make -j 2
 - ctest --verbose
 - ccache --show-stats