Update Medplum logo source in index.mdx (#3567)

Author: The-Alchemist

docs/pages/index.mdx

@@ -22,7 +22,7 @@ Special thanks to [Medplum](https://www.medplum.com/) for sponsoring node-postgr
 <a href="https://www.medplum.com/">
   <img
     alt="Medplum"
-    src="https://raw.githubusercontent.com/medplum/medplum-logo/refs/heads/main/medplum-logo.png"
+    src="https://raw.githubusercontent.com/medplum/medplum-logo/refs/heads/main/v3/medplum-logo-grape8-277x60.png"
     style={{
       width: '300px',
       height: 'auto',