The ornamental design for a blanket, as shown and described.
FIG. 1 is a front elevational view of a blanket, shown in flattened position of use. The broken lines showing the squares around the pictures, the phrases, and the bible verses are for illustrative purposes and form no part of the claimed design;
FIG. 2 is a top plan view, with the bottom plan view being a mirror image; and,
FIG. 3 is a left side elevational view taken from the left side of FIG. 1, with the right side elevational view being a mirror image.