update REPL core-js to 3.16
The core-js version in builtin REPL is out of dated, which is confusing users as in https://github.com/babel/babel/issues/13701.
This PR updates core-js version to latest 3.16, so features like String#replaceAll can be properly polyfilled.
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The preview REPL does not polyfill replaceAll either, I will investigate what is going on.
Superseded by https://github.com/babel/website/pull/2630.