Update "3.7. Creating Custom OAuth2 Protected Controllers"

[soraksh]

https://doc.cuba-platform.com/restapi-7.2/#rest_api_v2_custom_controllers

Change xlmns list from example from paragraph 2 from

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:security="http://www.springframework.org/schema/security"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
           http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd
               http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-4.2.xsd">

to

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:security="http://www.springframework.org/schema/security">