docs: make `Table of contents` as bold
diff --git a/docs/shared-mutable-state-and-concurrency.md b/docs/shared-mutable-state-and-concurrency.md
index 7530861..8591f17 100644
--- a/docs/shared-mutable-state-and-concurrency.md
+++ b/docs/shared-mutable-state-and-concurrency.md
@@ -15,7 +15,7 @@
 
 class SharedStateGuideTest {
 --> 
-## Table of contents
+**Table of contents**
 
 <!--- TOC -->