fix Matrix doc
@@ -255,7 +255,7 @@ func (r Rect) Union(s Rect) Rect {
// Matrix has a handful of useful methods, each of which adds a transformation to the matrix. For
// example:
//
-// pixel.IM.Moved(pixel.V(100, 200)).Rotated(0, math.Pi/2)
+// pixel.IM.Moved(pixel.V(100, 200)).Rotated(pixel.ZV, math.Pi/2)
//
// This code creates a Matrix that first moves everything by 100 units horizontally and 200 units
// vertically and then rotates everything by 90 degrees around the origin.
