Rewriting all routes in Vercel to the SPA handler

[mapra99]

fixes #29 Added a vercel.json file with configuration to serve all routes with the public/index.html file that contains our SPA, and from that point react-router will handle the route.

[vercel[bot]]

Deployment failed with the following error:

Rewrite at index 0 has invalid `source` pattern "/.*".

Learn More: https://vercel.link/invalid-route-source-pattern

[vercel[bot]]

Deployment failed with the following error:

Rewrite at index 0 has invalid `source` pattern ".*".

Learn More: https://vercel.link/invalid-route-source-pattern

[vercel[bot]]

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[vercel[bot]]

Deployment failed with the following error:

Invalid vercel.json file provided