The ornamental design for a holder for vehicles, as shown and described.
FIG. 1 is a perspective view of a holder for vehicles showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing of portions of the holder for vehicles is included for the purpose of illustrating environmental structure and forms no part of the claimed design.