[editorial] Add missing semicolons in example CSP (#619)

Author: antosart

index.bs

@@ -5008,7 +5008,7 @@ this algorithm returns normally if compilation is allowed, and throws a
       [[!HTML]]
 
       <pre>
-        <a http-header>Content-Security-Policy</a>: img-src 'none' script-src 'none' font-src 'none'
+        <a http-header>Content-Security-Policy</a>: img-src 'none'; script-src 'none'; font-src 'none'
       </pre>
 
       Supplementing this policy with `default-src 'none'` would improve the page's robustness