Timeout default of '0' breaks powershell

*This is either a puppet-sys issue or a powershell provider issue, unclear*:

with the [recent powershell module fix](https://github.com/puppetlabs/puppetlabs-powershell/pull/321) to support the timeout parameter of `exec`, execution of `sys::fetch` fails with the default `timeout` of `'0'`:

```
Debug: /Stage[main]/Windows::Nssm/Sys::Fetch[download-nssm]/Exec[fetch-download-nssm]/creates: Checking that 'creates' path 'C:\ProgramData\installers\nssm-2.24.zip' exists
Error: Failure waiting for PowerShell process 6044 to start pipe server
Error: /Stage[main]/Windows::Nssm/Sys::Fetch[download-nssm]/Exec[fetch-download-nssm]/returns: change from 'notrun' to ['0'] failed: Failure waiting for PowerShell process 6044 to start pipe server (corrective)
```

**0** should be **unlimited**, but, since it is a string, powershell provider interprets it as a non-false value (my guess). When overriden like this, everything works:

```puppet
Sys::Fetch{
timeout => 120, # a smaller number also works
}
# 0 doesn't seem to work though, unclear why.
```