updates visual rec example for iam

Author: anweshan

README.md

@@ -554,8 +554,9 @@ var VisualRecognitionV3 = require('watson-developer-cloud/visual-recognition/v3'
 var fs = require('fs');
 
 var visualRecognition = new VisualRecognitionV3({
-  api_key: '<api_key>',
-  version: '2016-05-20'
+  url: '<service_url>',
+  version: '2018-03-19',
+  iam_apikey: '<iam_api_key>',
 });
 
 var params = {