Consider removing polyfills, specifically, the one for Map from core-js

[ivan-aksamentov]

I believe that libraries should not impose polyfils on their downstreams. Anyways, It is rarely needed in node libraries, and especially in test environments. Instead, it is user's responsibility to ensure that their runtime supports all the necessary features.

Consider removing this Map polyfill:

redux-saga-test-plan/src/utils/Map.js

Line 4 in 7f78a07

: require('core-js/library/es6/map'));

Map was mostly supported since Node 0.12 and is fully supported since Node 6. We are now on 12 LTS, so I think it is safe to remove this polyfill.

Along with it core-js dependency can be removed, along with the warning that it produces:

warning redux-saga-test-plan > [email protected]: core-js@<3.0 is no longer maintained and not recommended for usage due to the number of issues. Please, upgrade your dependencies to the actual version of core-js@3.

Thanks a lot for this great library!