use constant for example

g-may · web-flow · commit 9bd6c78565b9 · 2017-03-03T17:06:48.000-05:00
diff --git a/README.md b/README.md
@@ -411,7 +411,7 @@ var NaturalLanguageUnderstandingV1 = require('watson-developer-cloud/natural-lan
 var nlu = new NaturalLanguageUnderstandingV1({
   username: '<username>',
   password: '<password>',
-  version_date: '2017-02-27'
+  version_date: 'NaturalLanguageUnderstandingV1.VERSION_DATE_2017_02_27'
 });
 
 nlu.analyze({
