Update linesegment.py

Make method str() to an overwritten operator __str__()

linesegment.py

@@ -60,7 +60,7 @@ class LineSegment:
     def get_max_y(self):
         """Get the highest y coordinate of the line segment"""
         return max(self.__startpoint.get_y(), self.__endpoint.get_y())
-    def str(self):
+    def __str__(self):
         """Return the line segment values as string."""
         return self.__startpoint.str() + "-->" + self.__endpoint.str()
     def draw(self):