Re,
Without any knowledge about npm I was wild-guessing from the error message
I've got from this command line I should rather use:
npm install --omit=dev
Did you try with : $ npm install --production=false--omit=dev should do the reverse, omitting dev dependencies needed for bundling (such as webpack). If it still doesn't work, maybe not using apt-get to install webpack and node-webpack-merge, but only relying on the "npm install" instruction to do it could help...
If it still doesn't work I'll try to do it in a fresh debian install in a VM when I find the time.
Thanks ! Julien