Summary:
Currently in the Flipper network plugin implementation, XMLTextFormatter is only enabled if `content-type` is `text/html`.
We should enable it for `application/xml` and `text/xml` as well.
Reviewed By: mweststrate
Differential Revision: D37733487
fbshipit-source-id: f272c5d0a305cf4afd32701d40459c3e11049886