The ornamental design for a shower ring, as shown and described.
FIG. 1 is a front perspective view of a shower ring showing my new design,
the woman shown in broken lines is for illustrative purposes only and
forms no part of the claimed design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof; and
FIG. 4 is a side elevational view thereof.
The broken lines on the shower ring shown in FIGS. 1-3 are understood to
represent conventional stitching.