get-builds endpoint is returning the wrong content-type

[ae6rt]

It should return application/json:

 curl -i http://192.168.99.100:31000/api/v1/builds/ae6rt/dynamodb-lab && echo

HTTP/1.1 200 OK
Access-Control-Allow-Headers: DECAP-APP-NAME, DECAP-API-TOKEN, Cache-Control, Pragma, Origin, Authorization, Content-Type, X-Requested-With
Access-Control-Allow-Methods: GET, PUT, POST, DELETE, OPTIONS
Access-Control-Allow-Origin: http://localhost:9000
Date: Sun, 09 Apr 2017 15:01:26 GMT
Content-Length: 302
Content-Type: text/plain; charset=utf-8

{"builds":[{"id":"0df70cb1-c6ce-418f-9c80-8fe3fd234c79","projectKey":"ae6rt/dynamodb-lab","branch":"master","result":0,"duration":0,"startTime":1491571627},{"id":"99e4ed8a-92e8-45c7-b80d-4592b51a98e4","projectKey":"ae6rt/dynamodb-lab","branch":"master","result":0,"duration":0,"startTime":1491570756}]}

[ae6rt]

fixed