install dependencies for the outer project too

Without the additional `npm install` step, gulp prints several instances of:

```
[16:04:57] gulp-notify: [Compile Error] Cannot find module 'react/addons' from '/Users/tom/src/material-ui/src/js'
```

and the page that opens has no content.
Merge pull request #69 from alltom/patch-1

install dependencies for the outer project too