Drop support of IE11

[juergba]

Description

We drop support of Internet Explorer 11.

• mocha.js: browser bundle transpiled to ES5 is dropped
• mocha-es2018.js: browser bundle in ES2018 is renamed to mocha.js

Description of the Change

devDependencies	from	to
@babel/preset-env	removed
@rollup/plugin-babel	removed
core-js	removed
regenerator-runtime	removed
rollup	2.66.0	2.70.1
@rollup/plugin-commonjs	14.0.0	21.0.2
@rollup/plugin-multi-entry	3.0.1	4.0.1
@rollup/plugin-node-resolve	8.4.0	13.1.3
rollup-plugin-visualizer	5.5.4	5.6.0
rollup-plugin-node-polyfills	replaced		rollup-plugin-polyfill-node

[juergba]

@giltayar do we still need to create/publish a sourcemap of our ES2018 browser bundle?
We don't transpile anymore, so I think we don't, right?

[giltayar]

@juergba while we don't transpile anymore, we still bundle, so theoretically a source map is still needed.

[juergba]

@giltayar ok, thanks. I will keep the source map then.