Update app.js

@@ -84,13 +84,15 @@ async function handleEvent(event) {
     return new Promise(async(resolve,reject)=>{  
       var file;
       
-      client.getMessageContent(event.message.id)
-      .then(async(stream) => {
+      await client.getMessageContent(event.message.id)
+      .then(
+        async(stream) => {
           await stream.on('data', (chunk) => {
-               file=chunk;
+            file = chunk;
             console.log(chunk);
           });
-      });
+        }
+      );
         console.log(file);
       var cheerio = require('cheerio');
       var uriBase = 'https://koreacentral.api.cognitive.microsoft.com/vision/v2.1/ocr';