Fix wrong property reference to keys-to-sanitize in Javadoc

[lltx]

When I use the /actuator/configprops endpoint to get the @ConfigurationProperties bean details.

I want to show the sensitive configuration such as password. Since the official website documentation does not explain the detailed usage of configprops endpoint, reading the source code notes found that it is incorrect and cannot work

---

management:
  endpoint:
    configprops:
      keys-to-sanitize:
        - secret

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[pivotal-issuemaster]

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[snicoll]

@lltx good catch and thank you for making your first contribution to Spring Boot.