The ornamental design for the door for a shower cubicle, as shown and described.
FIG. 1 is a front perspective view of a first embodiment of the door for a shower cubicle invention;
FIG. 2 is a front perspective view of a first embodiment of the door for a shower cubicle invention with said door in the open position;
FIG. 3 is a rear perspective view of a first embodiment of the door for a shower cubicle invention;
FIG. 4 is a front elevation of a first embodiment of the door for a shower cubicle invention;
FIG. 5 is rear elevation of a first embodiment of the door for a shower cubicle invention;
FIG. 6 is a left side elevation of a first embodiment of the door for a shower cubicle invention;
FIG. 7 is a right side elevation of a first embodiment of the door for a shower cubicle invention;
FIG. 8 is a top plan view of a first embodiment of the door for a shower cubicle invention;
FIG. 9 is a bottom plan view of a first embodiment of the door for a shower cubicle invention; and,
FIG. 10 is a front perspective view of a second embodiment of the door for a shower cubicle invention.
Structure that is not part of the claimed design, but is considered necessary to show the environment in which the design is associated, is represented in the drawings by broken lines.