[docs] fixed typos (#1211)
[docs] fixed typos (#1211)

* fixed typo

* fixed render of default value of metric param

* fixed typos

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