Bump to 4.0.0 nodejs puppet module

By using the new module, we aren’t restricted in having to wait for new
versions to be added to the puppet module. Instead, we can just define

```
nodejs::version { ‘v0.10.33`: }
```

Or possibly even

```
nodejs::version { ‘v0.11.14`: }
```

if you’re feeling adventurous!
Merge pull request #130 from alphagov/bump-nodejs-module

Bump to 4.0.0 nodejs puppet module