The ornamental design for an adjustablepillow, as shown and described.
FIG. 1 is a right side perspective view of the adjustable pillow; FIG. 2 is
a left side perspective view thereof; FIG. 3 is a top view thereof; FIG. 4
is a bottom view thereof; FIG. 5 is a front view thereof; and, FIG. 6 is a
rear view thereof.