Consider wider CI recognition

[yomed]

Hi, I noticed that the postinstall script attempts to recognize CI before showing the banner. It would be great if this supported a wider range of CI services, since not all of them use the CI environment variable.

core-js/packages/core-js/postinstall.js

Line 8 in 5a66505

var CI = is(env.CI);

There are packages that help support more CI services:
https://github.com/watson/ci-info#api

I can submit a PR if we are ok making this change. Thanks!

[zloirock]

The problem that core-js should follow a zero-dependency policy. However, I'll take a look at this, thanks. You can create a PR for the usage of those practices.

[zloirock]

Feel free to improve it.

[yomed]

Thank you!