Fix typo

Json -> JSON

Author: changeworld

articles/event-grid/authenticate-with-namespaces-using-json-web-tokens.md

@@ -131,7 +131,7 @@ az resource update \
  
 ```
 ## JSON Web Token format
-Json Web Tokens are divided into the JWT Header and JWT payload sections.
+JSON Web Tokens are divided into the JWT Header and JWT payload sections.
 
 ### JWT Header