Upgrade Node.js LTS Version and package.json Update

[jimmywarting]

I suggest that we consider upgrading the existing Node.js LTS version within the Istanbul project. This would allow us to take advantage of the latest enhancements and security updates. Additionally, it's worth considering an update to our package.json file to specify a higher engine.node version.

Advantages:

1. Improved Performance: The newer LTS versions come with optimizations that can significantly enhance the speed of our code execution.

2. Enhanced Security: An upgrade would ensure that we promptly address any potential vulnerabilities, thereby upholding the trust of our users.

3. Access to Modern Features: This upgrade would grant us access to new features of Node.js, facilitating more efficient development and the creation of cleaner code.

4. Sustained Support: LTS versions provide a stable foundation with ongoing support, minimizing the need for disruptive upgrades.

5. Streamlined Collaboration: Using a common Node.js version simplifies collaboration and aids in the smooth onboarding of contributors.

6. Removal of dependencies/polyfills: with new access to features of Node.js we don't need as many dependencies