`isNode` checks for the node version in which the process is running and it checks for the node key inside the versions. This is exactly the same as using `process.version` as they are set in the native code and `process.version` is just a shorthand for `process.versions.node`.
Previously Node.js was detected by the lack of `global.document` which doesn’t work in case JSDOM is being used in Node.js. Instead, we now detect `process.versions.node`, like here: 426943ae93 (diff-168726dbe96b3ce427e7fedce31bb0bc).
Fixes#6147.
DOMWorld only needs to use Node's `fs` module if you're adding a
filepath as a script/style tag. We can detect this case and run the
`require` inline such that in a browser this code won't execute.
