Update app.js

@@ -83,15 +83,14 @@ async function handleEvent(event) {
   else if (event.type == 'message'&& event.message.type == 'image') {
     return new Promise(async(resolve,reject)=>{  
       var file;
-      while(file!=undefined)
-    {
+      
       client.getMessageContent(event.message.id)
-      .then((stream) => {
-        stream.on('data', (chunk) => {
+      .then(async(stream) => {
+        await stream.on('data', (chunk) => {
                file=chunk;
         });
       });
-    }     
+        
       var cheerio = require('cheerio');
       var uriBase = 'https://koreacentral.api.cognitive.microsoft.com/vision/v2.1/ocr';
        var options = {