I claim the ornamental design for an earphone, as shown and described.
FIG. 1 is a perspective view of an earphone, showing our new design;
FIG. 2 is a bottom view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is a side view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a back view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design while all other broken lines are directed to environment that forms no part of the claimed design.