I recently updated to Eleventy 2.0 and received an error that "build.command" failed when I pushed the changes to Netlify. Vague errors are always fun. With a little research I was able to determine the default node version Netlify provides is not new enough to support the Eleventy upgrade. I found an article by Dan Urbanowicz very helpful to manually set the node version for Netlify builds. Initially I set an environmental variable through the UI but I just had a feeling I would forget and lose track of where that was being set. Using the .toml file will bring more visibility.