Fix duplicated id

Author: bonjourmauko

openfisca_web_api/openAPI.yml

@@ -370,7 +370,7 @@ paths:
       tags:
       - "Entities"
       summary: "List all available Entities"
-      operationId: "getVariables"
+      operationId: "getEntities"
       responses:
         200:
           description: "The list of the entities as well as their information is sent back in the response body"