fix(responseBody): json response highlighting (#6871)

Refs #6508 

* Add language prop to HighlightCode component

* Use language prop for JSON HighlightCode responses in response-body.jsx

src/core/components/response-body.jsx

@@ -94,13 +94,15 @@ export default class ResponseBody extends React.PureComponent {
       // Anything else (CORS)
     } else if (/json/i.test(contentType)) {
       // JSON
+      let language = null
       try {
         body = JSON.stringify(JSON.parse(content), null, "  ")
+        language = "json"
       } catch (error) {
         body = "can't parse JSON.  Raw result:\n\n" + content
       }
 
-      bodyEl = <HighlightCode downloadable fileName={`${downloadName}.json`} value={ body } getConfigs={ getConfigs } canCopy />
+      bodyEl = <HighlightCode language={language} downloadable fileName={`${downloadName}.json`} value={ body } getConfigs={ getConfigs } canCopy />
 
       // XML
     } else if (/xml/i.test(contentType)) {