fix spelling

Author: duongau

articles/firewall/toc.yml

@@ -76,7 +76,7 @@ items:
       href: premium-features.md
     - name: Portal
       href: premium-deploy.md
-    - name: Cerficates
+    - name: Certificates
       href: premium-certificates.md
     - name: Enterprise CA Certificates
       href: premium-deploy-certificates-enterprise-ca.md