docs.af.pivotal.io->docs-ip.spring.io

The build conventions plugin does not support a property, so we must
override the configuration for docs.host to docs-ip.spring.io

Closes gh-9686

docs/manual/spring-security-docs-manual.gradle

@@ -15,6 +15,7 @@ remotes {
 	docs {
 		retryCount = 5 // retry 5 times (default is 0)
 		retryWaitSec = 10 // wait 10 seconds between retries (default is 0)
+		host = "docs-ip.spring.io"
 	}
 }