Parse to json the response_body

[MiguelSavignano]

If the Content type of the response it's application/json It's better to parse as JSON, because some Logs Viewer can filter in this json payloads.

This prevents have a responseBody like this.

{ data: "{ foo: 'baz' }" }

[trusche]

Thanks, and sorry for the late reply. I'm closing this in favour of #85, feel free to re-open if that doesn't solve your issue.