The ornamental design for an earphone, as shown and described.
FIG. 1 is a perspective view of an earphone;
FIG. 2 is a front view thereof,
FIG. 3 is a rear view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof.;
FIG. 6 is a right side view thereof; and,
FIG. 7 is a left side view thereof.
The broken lines showing on the drawing disclosure are for illustrative purposes only and form no part of the claimed design.