We claim the ornamental design for a beverage insulator, as shown and described.
FIG. 1 is a perspective view of a beverage insulator showing the new design;
FIG. 2 is a side view thereof;
FIG. 3 is an opposite side view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a rear view thereof.
The dashed lines appearing on the beverage insulator are indicative of stitching. The broken lines of the can are for illustrative purposes only and form no part of the claimed design.