The ornamental design for a rockingchair, as shown and described.
FIG. 1 is a perspective view of a rocking chair showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a top view thereof.
A bottom view thereof is omitted since it does not contain ornamental features. The heavy broken line showing of stitch lines forms portions of the claimed design, while the light broken line showing of portions of the rocking chair forms no part of the claimed design.