Hi Parveen,
As it is mentioned in this post, dhis2-cdn.org is not working. you should download that chart.js file from the instance you are getting the chart from (e.g. https://play.dhis2.org/2.30/dhis-web-visualizer/chart.js) as It couldn’t be referenced directly from the script tag (security issues).
and one last thing you need to make sure of, is check if your browser web security is disabled else it will block you from accessing dhis2 resources.