Add 'events' dependency

[ooflorent]

webpack/hot/emitter.js requires events.
This package used to be polyfilled automatically.
Now it requires the dependency to be manually installed.

What kind of change does this PR introduce?

bugfix

Did you add tests for your changes?

no

Does this PR introduce a breaking change?

no

What needs to be documented once your changes are merged?

nothing

[webpack-bot]

For maintainers only:

• This need to be documented (issue in webpack/webpack.js.org will be filed when merged)

[webpack-bot]

Thank you for your pull request! The most important CI builds succeeded, we’ll review the pull request soon.

[sokra]

Thanks