add newline to /readiness success response

While rolling config changes to pages pages, I was checking the boot status of the service via:

ssh web-pages-02-sv-gprd.c.gitlab-production.internal curl -s localhost:1080/-/readiness

In a loop.

The "not yet ready" response includes a newline, but the success one does not.

That created output like this:

not yet ready
not yet ready
not yet ready
not yet ready
successsuccesssuccesssuccesssuccesssuccesssuccess

This patch adds a newline for this use case.