Fix substring error when downloading

[dontrolle]

> Test-NvidiaDriver -Download
MethodInvocationException: C:\src\Powershell\nvidiadrivercheck.psm1:134
Line |
 134 |      $installedString = ($installedDriverVersion -replace "\.").Substr …
     |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     | Exception calling "Substring" with "2" argument(s): "Index and length must refer to a location within
     | the string. (Parameter 'length')"

It looks like there's a more recent driver available.
Downloading to your Downloads folder at [...]