ESM modules aren't registered in package.json

[fabis94]

Describe the bug
Even though this package comes with an ESM version, it's not clear to me how build tools are supposed to pick up on it, when the ESM modules aren't specified anywhere in the package.json. Out of 'main', 'module' and 'exports' only the 'main' field is filled out and it links to day.min.js, which is not ESM.

Expected behavior
Package.json should be updated to point to the modules inside ./esm/ through the module and exports fields

Information
irrelevant

[Bykiev]

Hi, it seems to be really a bug and build tools most probably will use it as commonJS module. Can you please create a PR to fix it?

Upd: here is a discussion about esm support: #1765 , #1528