No longer compiles - spring-boot-actuator-docs module has been removed

Since the M7 update (from M3) this no longer compiles ([Updated to Spring Boot 2.0.0.M7](https://github.com/springframeworkguru/reactive-sandbox/commit/aa435fbe741c6bb54a0da0ce16ca55aede9bd5a1)).

The `spring-boot-actuator-docs` module no longer exists: [Remove separate spring-boot-actuator-docs module](https://github.com/spring-projects/spring-boot/issues/9899).