Fix docstring example for Vector.rotate
Fix docstring example for Vector.rotate

Previously example incorrectly showed that Vector gets rotated in place.
This fixes the docstring to show that a new vector is returned.

akshayaurora/kivy,inclement/kivy,kivy/kivy,kivy/kivy,rnixx/kivy,matham/kivy,akshayaurora/kivy,akshayaurora/kivy,matham/kivy,rnixx/kivy,kivy/kivy,rnixx/kivy,matham/kivy,inclement/kivy,matham/kivy,inclement/kivy