Uncaught Error: Cannot find module "promise-polyfill/lib/polyfill"

[Mohinesh27]

Hi I am completely new to Ionic and firebase. So for my personal interest, I am trying to run this repo on my machine. I followed all steps about chat21-ionic app and functions and it is deployed as per the directions. But when I am trying to run ionic serve I am getting error Uncaught Error: Cannot find module "promise-polyfill/lib/polyfill"

For reference -

Thanks in advance