update section title

Author: zhiyuanliang-ms

articles/azure-app-configuration/TOC.yml

@@ -300,7 +300,7 @@
           href: ./rest-api-throttling.md
         - name: Versioning
           href: ./rest-api-versioning.md
-  - name: Client libraries
+  - name: Configuration providers
     items:
     - name: Overview
       href: ./configuration-provider-overview.md