Determine minimum Node version requirement

[TheJaredWilcurt]

Some language features did not exist in older versions of Node, and some dependencies may be using those.

Need to manually test (when the library is in a more stable state) older node versions to see which ones are supported.

There seems to be a big difference between 8.0.0 and 8.3.x. Most of my libraries end up being 8.3+. But would like to at least document the lowest version.

Note: Dependency support for that version matters. devDependencies support does not.

[stemount]

@TheJaredWilcurt How about using your GitHub action run the same tests on different Docker image containers to do this in an automated way - this adds regression testing for older versions of Node!!!! #27

[TheJaredWilcurt]

Eventually, yes, the lowest supported version will be listed in the Node version matrix in the GitHub Actions yml. However first we need to get the library to a more stable point, then manually test the versions with nvm to see which ones are supported, and if changing a line or two of code would allow us to support older versions. Once we've found that information, it can be stored in the README as a badge and in the GH Actions file to ensure the version support is not dropped.