logging API returns logfmt format regardless of header

when executing GET /kapacitor/v1preview/logs
Content-Type: application/json

I always get logfmt format back...

root@devdatacenter-kapacitor-0:/# curl --header "Content-Type: application/json" localhost:9092/kapacitor/v1preview/logs
ts=2018-08-08T20:48:19.626Z lvl=info msg="created log session" service=sessions id=cd1e7a68-a6d0-4a5f-9a0d-d7842e2ecca0 content-type=application/logfmt
...

2018/08/08 19:57:47 Using configuration at: /etc/kapacitor/kapacitor.conf
ts=2018-08-08T19:57:47.978Z lvl=info msg="kapacitor starting" service=run version=1.5.0 branch=HEAD commit=ee0d8bc17a01a3321d7d44eb5ee8e1156c3d5ec6
ts=2018-08-08T19:57:47.978Z lvl=info msg="go version" service=run version=go1.10.2

Reproduce the GET /kapacitor/v1preview/logs request with the curl command and inspect the handler for that endpoint. Determine how the request header is used to select the response format; done means the API returns the format requested by the client instead of always returning logfmt.

Written by the indexing model from the issue text.