Update index.md

prevent SyntaxError: Octal literals are not allowed in strict mode.

docs/index.md

@@ -23,7 +23,7 @@ var User = sequelize.define('User', {
 return sequelize.sync().then(function() {
   return User.create({
     username: 'janedoe',
-    birthday: new Date(1980, 06, 20)
+    birthday: new Date(1980, 6, 20)
   });
 }).then(function(jane) {
   console.log(jane.get({