"module.js:549 throw err; ^ Error: Cannot find module '@babel/polyfill'"

When running node generate-site.js site/ as per the README, I get:

module.js:549
    throw err;
    ^

Error: Cannot find module '@babel/polyfill'
    at Function.Module._resolveFilename (module.js:547:15)
    at Function.Module._load (module.js:474:25)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (/root/vitrine/generate-site.js:1:63)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3