I agree with you and thanks for sharing your wisdom. Apart from running prune when running the windows installer, prior to packaging I also ran npm prune 'any_module' I wasn't using and I think there is still a few more to remove.
One of my aims in making this app was to use core Node.js modules, in this case https and fs. I could have used request or express but I didn't. On top of that I did install electron(of course) and moment.js - and because I had to, electron-packager and electron-winsinstaller and Wine because I'm on Linux.
Refactored some lengthy code, got rid of any empty lines, unnecessary comments, white space and so on. Fundamental stuff and whether that made a huge difference I believe so - every byte helps.
I'll admit I am not an experienced dev but I am sticking with Node.js and Electron because I like it and I know there will always someone more experienced willing to advise.