[ci] fix macOS builds at Travis (#1560)
[ci] fix macOS builds at Travis (#1560)


microsoft/LightGBM,microsoft/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,henry0312/LightGBM,henry0312/LightGBM,henry0312/LightGBM