update

Author: Y-Sindo

articles/azure-web-pubsub/toc.yml

@@ -144,7 +144,7 @@
           href: howto-troubleshoot-common-issues.md
     - name: Move across regions
       href: howto-move-across-regions.md
-- name: MQTT(Preview)
+- name: MQTT (Preview)
   expanded: false
   items:
     - name: Overview