FIG. 1 is a top perspective view of a beverage container showing my new design. FIG. 2 is a bottom perspective view thereof. FIG. 3 is a front view thereof. FIG. 4 is a right side view thereof. FIG. 5 is a rear view thereof. FIG. 6 is a left side view thereof. FIG. 7 is a top plan view thereof; and, FIG. 8 is a bottom plan view thereof. The broken lines are for illustrative purposes only and form no part of the claimed design.