markdown-styles missing from `package.json`

[sumbach]

To build the book locally, I needed to add the "markdown-styles" package to package.json. I suspect you have this globally install (since you wrote it!)

[sumbach]

Related: I added the following at the top of Makefile to get the build to work without modifying specifying PATH on the command line:

SHELL:=/bin/bash
PATH:=node_modules/.bin:$(PATH)