I claim the ornamental design for a vent cap, as shown and described.
FIG. 1 is a perspective view of the vent cap from above.
FIG. 2 is a perspective view of the vent cap from below.
FIG. 3 is the front elevational view thereof.
FIG. 4 is the right side elevational view thereof.
FIG. 5 is a rear elevational view.
FIG. 6. is the left side elevational view thereof.
FIG. 7 is a top plan view; and,
FIG. 8 is a bottom plan view.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.