upgrade core-js

[xfumihiro]

warning: core-js@<2.6.8 is no longer maintained. Please, upgrade to core-js@3 or at least to actual version of core-js@2.

[ckruse]

warning: core-js@<3 is no longer maintained and not recommended for usage due to the number of issues.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.

[ckruse]

Is this project dead?

[ckruse]

warning @absinthe/socket-apollo-link > core-js@2.6.0: core-js@<3.3 is no longer maintained and not recommended for usage due to the number of issues. Because of the V8 engine whims, feature detection in old core-js versions could cause a slowdown up to 100x even if nothing is polyfilled. Please, upgrade your dependencies to the actual version of core-js.