The ornamental design for a gameboard, as shown and described.
FIG. 1 is a plan view of a game board in accordance with a first embodiment of the present design and lined for color; and,
FIG. 2 is a plan view of a game board in accordance with a second embodiment of the present design.
In FIG. 1, the vertically lined area is shaded to represent the color red, and vertical crosshatched areas are shaded to represent the color black. FIG. 2 is shaded for no specific color.