The ornamental design for a monitor, as shown and described.
FIG. 1 is a front perspective view of a monitor showing our new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a rear perspective view thereof.
The short dash-dash lines that are immediately adjacent the shaded areas and define unshaded regions represent the bounds of the claim and are not included in the claim. All other short dash-dash broken lines are directed to environment and are for illustrative purposes only. All of the broken lines throughout the views form no part of the claimed design.