Replace deprecated packages & update dependencies

[oscarvz]

The repo currently contains abandoned/deprecated libraries which are replaced with their up-to-date version in this PR.

• babel-eslint is deprecated and replaced with actively maintained @babel/eslint-parser;
• rollup-plugin-babel is deprecated and replaced with actively maintained @rollup/plugin-babel. Updated .rollup.js according to the plugin's requirements;
• Update all other packages to their minor/patch update versions.

Other things to note:

• I added the generated yarn.lock file as there was no lockfile available in the repo. I'll be happy to generate a package-lock.json file if that is preferred;
• I noticed some formatting inconsistencies in the files; I'll be happy to run a code formatter to fix these issues.

[oscarvz]

@jonathantneal apologies for pinging you as I'm sure you're very busy. It seems you're the only one who can review this and bump the NPM package, and there isn't a lot of recent activity in this repo.
Is there any chance you could look at this and bumpp the NPM package? Thank you so much!