The ornamental design for a travel bib, as shown and described.
FIG. 1 is a front elevational view of a travel bib showing my new design;
FIG. 2 is a rear elevational view thereof, the broken lines being understood to represent environmental subject matter that forms no part of the claimed design;
FIG. 3 is a top plan view thereof.
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is a left side elevational view thereof, the right side elevational view being a mirror image of the left side view.