change content-type GET workflow/{workflow-id} according to POST /workflow

[joschrew]

In POST /workflow (upload a workflow-script) the content-type is text/vnd.ocrd.workflow. Because of that I think the content type to get back a workflow must be the same and not application/vnd.ocrd+zip.

[joschrew]

Reminder (rather for myself) to know what I mean:
POST /workflow is used to upload a workflow. There the content-type for the request body is text/vnd.ocrd.workflow. I assume this is right.
GET /workflow/{workflow-id} us used to retrieve a workflow. There the content-type of the response is currently application/vnd.ocrd+zip. But it returns a workflow and not a workspace so I think the content-type has to be changed to one mentioned before. I think this is just a copy-and-paste leftover, where the creator forgot to change the type of the response.