--publish: use banner provided by server

[vincent-psarga]

The messages.cucumber.io server responds with the banner as part of the 202 pesudo-redirect response. We should use it instead of computing our own like we do in cucumber-js#1424.

Advantages:

• people can override CUCUMBER_PUBLISH_URL and no longer get a banner pointing to reports.cucumber.io
• server implementation can provide their own banner
• no need to release new cucumber-ruby when changing the wording/styling of the banner or location of the report web app
• more consistency between cucumber implementations