The ornamental design for a hearingaid, as shown and described.
FIG. 1 is a top prospective view of a hearing aid showing my new design.
FIG. 2 is a front view thereof.
FIG. 3 is a back view thereof.
FIG. 4 is a top view thereof.
FIG. 5 is a bottom view thereof.
FIG. 6 is a side view thereof; and,
FIG. 7 is front view thereof shown in condition of use with a like hearing aid. The broken lines in FIG. 7 represent environmental subject matter and form no part of the claimed design.