npm instead of yarn in node-js-server-guide.md

[udofia2]

What/Why/How?

yarn intall --save express-session express express-async-errors morgan //typo

npm install --save express-session express express-async-errors morgan //correct

Reference

node-js-server-guide.md

Testing

Screenshots (optional)

Check yourself

• [ x] Code is linted
• [ x] Tested
• [ x] All new/updated code is covered with tests

Security

• [ x] Security impact of change has been considered
• [ x] Code follows company security practices and guidelines