[colors] fix: output lib/cjs and lib/esm modules

[adidahiya]

Changes proposed in this pull request:

@blueprintjs/colors was set up with a nonstandard /lib folder from the beginning. This PR updates the build outputs to match the other @blueprintjs packages.

Submodule paths are not part of our public API (users shouldn't be reaching into /lib/ manually), so it's not a breaking change.

[adidahiya]

[colors] fix: output lib/cjs and lib/esm modules

Build artifact links for this commit: documentation | landing | table | demo

This is an automated comment from the deploy-preview CircleCI job.

[shim-flounce]

Hm for some reason this now results in tslib being pulled in where previously this was just Object.assign. Check line 16 of https://unpkg.com/browse/@blueprintjs/colors@4.2.0/lib/esm/colors.js and 131 of https://unpkg.com/browse/@blueprintjs/colors@4.1.24/lib/colors.js

With strict package managers such as Yarn in PnP mode this won’t work because the colors package doesn’t list tslib as a dependency.

[shim-flounce]

I believe this is caused by this. Instead of targeting ES2015, it now targets ES5.

[adidahiya]

I'll add in the tslib dependency. It's better for the packages to be consistent. We can consider migrating to "target": "es2015" in a future major version.