Update app.js

@@ -97,7 +97,7 @@ async function handleEvent(event) {
           language: 'en'
           language: 'en'
         },
         },
         headers: {
         headers: {
-          'Content-Type': 'application/octet-stream',
+          'Content-Type': 'application/json',
           'Ocp-Apim-Subscription-Key': '979dc5d63344438fa4701c62feebb7dc'
           'Ocp-Apim-Subscription-Key': '979dc5d63344438fa4701c62feebb7dc'
         },
         },
         body: chunk
         body: chunk