[docs] Minor fixes (#1163)

docs/Features.rst

@@ -26,6 +26,7 @@ Following are advantages for histogram based algorithms:
    -  To get one leaf's histograms in a binary tree, can use the histogram subtraction of its parent and its neighbor
 
    -  So it only need to construct histograms for one leaf (with smaller ``#data`` than its neighbor), then can get histograms of its neighbor by histogram subtraction with small cost (``O(#bins)``)
+   
 -  **Reduce memory usage**
 
    -  Can replace continuous values to discrete bins. If ``#bins`` is small, can use small data type, e.g. uint8\_t, to store training data