Fix npm backup issue #226

[nick-The-One]

This change solves issue #226 by using json format for dumping npm dependencies and parcing its keys — should be more robust than split by slash.

[nick-The-One]

@alichtman Hey there! Could you take a look at this PR?

[alichtman]

Hey, thanks for the ping + patience. [Insert not enough time to do everything I want to do spiel].

I agree this PR is worthwhile. Thanks for taking the time to write it!

See the pointer to where changes are required for the reinstallation process. I'd love to have some automated end-to-end testing to make sure changes like this don't break anything.

Edit: Thought about it further; I'm not sure if any changes are required. Let me take another look when I get back to my computer. I wrote this code almost half a decade ago, and it's not super fresh in my mind anymore.

Edit 2: Yep, this seems to work as expected! Disregard v1 of my comments.

Cheers :)
Aaron