mock-api: wrong content-type

[Emilgardis]

twitch-cli version: twitch-cli/source (9370e1a)

curl -X GET "http://localhost:8080/units/categories" --header "accept: application/json" -v

sends data with header Content-Type: text/plain; charset=utf-8

curl -X POST "http://localhost:8080/auth/token?client_id=mockid&client_secret=mocksecret&grant_type=client_credentials" --header "Accept: application/json" -v

also sends data with header Content-Type: text/plain; charset=utf-8

curl.exe -X GET "http://localhost:8080/mock/users" --header "Accept: application/json" --header "Authorization: Bearer mytoken" --header "Client-ID: mymockid" -v

returns Content-Type: application/json correctly

[lleadbet]

Meant to re-add this; will fix in the coming week or two.