modernize & improve the example in readme.md (#81)

readme.md

@@ -19,19 +19,22 @@ Install:
 Example:
 ====
 ```javascript
-var DOMParser = require('xmldom').DOMParser;
-var doc = new DOMParser().parseFromString(
-    '<xml xmlns="a" xmlns:c="./lite">\n'+
-        '\t<child>test</child>\n'+
-        '\t<child></child>\n'+
-        '\t<child/>\n'+
-    '</xml>'
-    ,'text/xml');
-doc.documentElement.setAttribute('x','y');
-doc.documentElement.setAttributeNS('./lite','c:x','y2');
-var nsAttr = doc.documentElement.getAttributeNS('./lite','x')
-console.info(nsAttr)
+const { DOMParser } = require('xmldom')
+
+const doc = new DOMParser().parseFromString(
+    '<xml xmlns="a" xmlns:c="./lite">\n' +
+        '\t<child>test</child>\n' +
+        '\t<child></child>\n' +
+        '\t<child/>\n' +
+        '</xml>',
+    'text/xml'
+)
+doc.documentElement.setAttribute('x', 'y')
+doc.documentElement.setAttributeNS('./lite', 'c:x', 'y2')
 console.info(doc)
+
+const nsAttr = doc.documentElement.getAttributeNS('./lite', 'x')
+console.info(nsAttr)
 ```
 API Reference
 =====