docs: use correct banner
-<h1 align="center"><img src="https://raw.githubusercontent.com/ory/meta/master/static/banners/oathkeeper.svg" alt="ORY Keto - Open Source & Cloud Native Access Control Server"></h1>
+<h1 align="center"><img src="https://raw.githubusercontent.com/ory/meta/master/static/banners/keto.svg" alt="ORY Keto - Open Source & Cloud Native Access Control Server"></h1>
<h4 align="center">
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