[fix] Rename schema file in standard extension name

rfc/0003 RFC GraphQL API for Duniter Clients.md

@@ -374,7 +374,7 @@ So the websoket channel path is automatically deducted from the optionnal path:
 
 ## API GraphQL Schema
 
-See [schema.gql](../appendices/0003_RFC/schema.gql)
+See [schema.gql](../appendices/0003_RFC/schema.graphqls)
 
 ---
 End of the document.

[Moul]

Is it intentional to have a s at the end, same for the name of the file?

It is recommended to use .graphql without the s at the end.