Okay, I just looked over the this “how-to-gutenberg-plugin” and there was an extra folder there. That may have been the problem.
When you download this plugin – https://github.com/zgordon/how-to-gutenberg-plugin
And install it, it will likely have a path like “../wp-content/plugins/how-to-gutenberg-plugin-master/” that is the directory you should run npm install in.
I just double checked it with both plugins and it worked. Not sure what the problem may be at this point, but let me know how this goes and we’ll work it out 👍