try to add the query parameter with output_mode=json.
https://<yourhost>:<mgnt_port>/.../../..?output_mode=json
Read this, http://docs.splunk.com/Documentation/Splunk/6.6.0/RESTTUT/RESTsearches
You can return search results in JSON, CSV or XML by setting the output_mode parameter. By default, results are returned in XML format.
For example, to retrieve search results in JSON format, make the following call.
Note: The curl listing includes --get because you are passing a parameter to a GET operation.
curl -u admin:changeme \
-k https://localhost:8089/services/search/jobs/1258421375.19/results/ \
--get -d output_mode=json