The ornamental design for a shower combo, as shown and described.
FIG. 1 is a front-right-top perspective view of a shower combo showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines and the area between the solid line and broken lines in FIGS. 3 & 7 represent portions of a shower combo and form no part of the claimed design.