Hi @Sujan12,
I did the changes as per your comments.
I have also installed nvm-windows which is of a great help.
When i tried to run the project after downgrading the npm i got this error :
PS D:\app> ionic cordova run android --prod --verbose
ERR: Your Node.js version is v5.0.0. Please update to the latest Node 6 LTS version (or latest Node).I am really stuck up now.