[fix] modernize the code

[aminya]

This PR update the code using modern JavaScript and also fixing some of the performance issues.

The first three commits were automatic using jscodeshift, and the last one was manual.

The tests passing:

[ghost]

Reviewing this tomorrow night 🤙🏼

[aminya]

The changes were quite straight forward and the tests are passing. Let me know if there is a question.

[jimmywarting]

next up: use nodes built in mkdir instead of the mkdirp package

[stianjensen]

Is there any interest in getting help getting this over the finish line?

I can also help updating or removing the old dependencies on mkdirp and rimraf.