Move `core-js` and `nanopop` dependencies to dev

[edoardocavazza]

Hi! I was wondering if it would be possible to move the core-js and nanopop dependencies to dev dependencies since the library is distributed as a bundle. This would avoid downloading unnecessary dependencies into projects.

Your environment:

Version (see Pickr.version): 1.9.1
Used bundle (es5 or normal one): normal
Used theme (default is classic): default
Browser-version:  -
Operating-system: -