Update security-authorization.md

Typo

docs/guide/security-authorization.md

@@ -306,8 +306,7 @@ For applications that require complex access control with dynamically updated au
 
 As aforementioned, rules add additional constraint to roles and permissions. A rule is a class extending
 from [[yii\rbac\Rule]]. It must implement the [[yii\rbac\Rule::execute()|execute()]] method. In the hierarchy we've
-created previously author cannot edit his own post. Let's fix it. First we need a rule to verify that the user is post
-author:
+created previously author cannot edit his own post. Let's fix it. First we need a rule to verify that the user is the post author:
 
 ```php
 namespace app\rbac;