[R-package] fixed NOTE about unrecognized global variable (#2928)
[R-package] fixed NOTE about unrecognized global variable (#2928)


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