0.51.2: the breadcrumb example is a chat provider's reply URL

The breadcrumb's example of a credential in a URL's path is a chat
provider's reply URL. Patch: wording in a docstring and a test, and
nothing is reversed.

Changed

• outgoing_breadcrumb's docstring and the privacy test that holds it
  take their example from a chat provider's reply URL, the address a
  copy posts to when it answers a chat command; the test posts to
  /commands/<credential> and asserts, as before, that the breadcrumb
  keeps the scheme and the host and no segment of the path.