rimraf: command not found
I thought I had followed all the instructions, but I'm getting an error when I try to build:

```
npm run build

> s1-ui@3.0.3 prebuild /Users/xxx
> rimraf dist

sh: rimraf: command not found
npm ERR! file sh
npm ERR! code ELIFECYCLE
npm ERR! errno ENOENT
npm ERR! syscall spawn
npm ERR! s1-ui@3.0.3 prebuild: `rimraf dist`
npm ERR! spawn ENOENT
npm ERR! 
npm ERR! Failed at the s1-ui@3.0.3 prebuild script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm WARN Local package.json exists, but node_modules missing, did you mean to install?

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/xxx
```
What am I missing?
