doc: broken link in Parameter Manager doc

[zhumin8]

spring-cloud-gcp/docs/src/main/asciidoc/parameter.adoc

Line 109 in f96a628

https://cloud.spring.io/spring-cloud-static/docs/1.0.x/spring-cloud.html#_endpoints[Spring Cloud] provides support to have configuration parameters be reloadable with the POST request to `/actuator/refresh` endpoint.