deployment/show endpoint returns JSON with content-type text/html

[renaudguerin]

This one should be trivial to fix, unfortunately I'm not in a position to set up a Grails dev environment at the moment and send that pull request, sorry :(

/[region]/deployment/show/[deploymentId].json correctly returns JSON content, but with text/html as the content-type.

It's a little annoying as I'm most relying on content-type to check for errors when using the deployment API (failures are typically returned as an HTML error page, and I haven't found HTTP error codes from Asgard to be very reliable : for instance the "proceed" endpoint returns 404 even upon success, see issue #584 )