Update kdbush to be a require module.

[bagnell]

Fixes #4418.

[pjcozzi]

Update CHANGES.md.

@chris-cooper could you please verify this?

[mramato]

I honestly think the warning @chris-cooper reported is a false positive. It's not really a pre-built javascript file, it just has the UMD boilerplate at the top so that it can be used in multiple different module loaders.

The main (and only) problem I have with this manual clean up that @bagnell did is that it means we have to do it every time we want to update to a new version of kdbush.

If we really want to "fix" this, we should be automatically grabbing the version from npm and doing whatever we need automatically during npm install. Of course this is a longer-term change I'd like to see where we use npm for front-end dependcies as well (for non-built versions).

Whatever you guys decide for now is fine with me, but we need to strive to be able to effortless update third party libraries on a regular basis.

[pjcozzi]

@mramato is right in general.

For now for this case, this change is fine since kdbush is pretty stable and has not had significant updates recently: https://github.com/mourner/kdbush/commits/master

@chris-cooper please merge once you confirm, thanks.

[pjcozzi]

@bagnell update CHANGES.md.

[chris-cooper]

Yes this makes the warning go away. I'm happy for it to be merged once @bagnell has updated CHANGES.md.

[bagnell]

@pjcozzi @chris-cooper CHANGES.md has been updated. This is ready.

[pjcozzi]

Thanks @bagnell @chris-cooper