Fix wrong reference to center_point attribute
"center_point" doesn't exist as dxf attribute of this class anymore and is now accessible as "center" attribute
@@ -50,7 +50,7 @@ Factory function :meth:`Drawing.viewports.new`
Upper-right corner of viewport
- .. attribute:: dxf.center_point
+ .. attribute:: dxf.center
View center point (in :ref:`DCS`)
