diff --git a/book.json b/book.json
index 1d8745407d11e069c8e72e511f940f9b5e532f78..ce90fce64a643d4f34940e9b12e7513221743e72 100644
--- a/book.json
+++ b/book.json
@@ -4,6 +4,6 @@
     "structure": {
         "readme": "index.md",
         "summary": "SUMMARY.md"
-    }
+    },
     "plugins": ["hints"]
 }