Install-SfbLabRequirements fails - incorrect function called

Install-SfbLabRequirements fails with multiple message like this one:
```
Get-LabMachine : The term 'Get-LabMachine' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included,
verify that the path is correct and try again.
At C:\Program Files\WindowsPowerShell\Modules\SfBAutomatedLab\0.6\SfBAutomatedLab.psm1:314 char:17
+ $machines = Get-LabMachine
+ ~~~~~~~~~~~~~~
+ CategoryInfo : ObjectNotFound: (Get-LabMachine:String) [], CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException

Install-LabWindowsFeature : Cannot validate argument on parameter 'ComputerName'. The argument is null or empty. Provide an argument that is not null or empty, and then try the command
again.
At C:\Program Files\WindowsPowerShell\Modules\SfBAutomatedLab\0.6\SfBAutomatedLab.psm1:315 char:45
+ Install-LabWindowsFeature -ComputerName $machines -FeatureName NE ...
+ ~~~~~~~~~
+ CategoryInfo : InvalidData: (:) [Install-LabWindowsFeature], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationError,Install-LabWindowsFeature
```
This is because Get-LabMachineDefinition should be used instead of Get-LabMachine.