"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
```
issue