The ornamental design for a shelter, as shown and described.
FIG. 1 is an upper front perspective view of a shelter of this invention in which a canopy includes a fixed end extending from a frame and has a free end for fluttering in the breeze;
FIG. 2 is lower rear perspective view of the shelter of FIG. 1;
FIG. 3 is front view of the frame of FIG. 1;
FIG. 4 is a rear view of the frame of FIG. 1;
FIG. 5 is a top view of the canopy and frame of FIG. 1;
FIG. 6 is bottom view of the canopy and frame of FIG. 1;
FIG. 7 is left side view of the canopy and frame of FIG. 1; and,
FIG. 8 is right side perspective view of the canopy and frame of FIG. 1.
The broken lines depict portions of the shelter that form no part of the claimed design. The dot-dot-dash broken lines depict a symbolic break in the article. The portion between the break lines forms no part of the claimed design.