Change the React Router logos on the homepage

The current Remix Router logos have no transparency so look ugly on on the homepage:

change the light image to the following: https://reactrouter.com/_brand/React%20Router%20Brand%20Assets/React%20Router%20Lockup/Light.svg

and the dark to this one: https://reactrouter.com/_brand/React%20Router%20Brand%20Assets/React%20Router%20Lockup/Dark.svg

Test that the change have been successful. 