[cookbook] Fix bug in .sample.env file (#87)

Remove trailing comma

Author: williamw

genai-cookbook/.sample.env

@@ -1,7 +1,7 @@
 COOKBOOK_ENDPOINTS='[
   {
-    "id": "max",
+    "id": "localhost",
     "baseUrl": "http://127.0.0.1:8000/v1",
-    "apiKey": "EMPTY",
+    "apiKey": "EMPTY"
   }
 ]'