The ornamental design for a microserver, as shown and described.
FIG. 1 is a front perspective view of a micro server including a front cover panel with a latching mechanism, the broken lines are shown for environmental purposes only and form no part of the claimed design;
FIG. 2 is a front, side perspective view thereof;
FIG. 3 is a front and opposite side perspective view thereof wherein the front cover panel is shown extended in a downward position; and,
FIG. 4 is a top, side and rear perspective view thereof.