The ornamental design for a sippybottle, as shown and described.
FIG. 1 is a perspective view of a sippy bottle showing my new design;
FIG. 2 is a front view of the sippy bottle;
FIG. 3 is a rear view of the sippy bottle;
FIG. 4 is a right side view of the sippy bottle;
FIG. 5 is a left side view of the sippy bottle;
FIG. 6 is a top view of the sippy bottle; and,
FIG. 7 is a bottom view of the sippy bottle.
The broken lines showing in the figures are included for the purpose of illustrating portions of the sippy bottle that form no part of the claimed design. The dash-dot lines showing in the figures are included for defining the bounds of the claimed design that form no part therof.