[ci] simplified and speeded up Travis (#1429)
[ci] simplified and speeded up Travis (#1429)


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