onboarding script doesn't work on windows

[jeremymanning]

error trace:

PS C:\Users\miles> irm https://raw.githubusercontent.com/ContextLab/lab-manual/master/scripts/setup.ps1 | iex
iex : At line:369 char:61
+ ...             $result = python -c "import $pkg; print(f' $pkg: {$pkg._ ...
+                                                           ~~~~~
Variable reference is not valid. ':' was not followed by a valid variable name character. Consider using ${} to
delimit the name.
At line:371 char:41
+                 Write-LogSuccess "  $pkg: OK"
+                                         ~~~~~
Variable reference is not valid. ':' was not followed by a valid variable name character. Consider using ${} to
delimit the name.
At line:374 char:41
+                 Write-LogWarning "  $pkg: FAILED"
+                                         ~~~~~
Variable reference is not valid. ':' was not followed by a valid variable name character. Consider using ${} to
delimit the name.
At line:378 char:37
+             Write-LogWarning "  $pkg: FAILED"
+                                     ~~~~~
Variable reference is not valid. ':' was not followed by a valid variable name character. Consider using ${} to
delimit the name.
At line:1 char:88
+ ... [busercontent.com/ContextLab/lab-manual/master/scripts/setup.ps1](http://busercontent.com/ContextLab/lab-manual/master/scripts/setup.ps1) | iex
+                                                                        ~~~
    + CategoryInfo          : ParserError: (:) [Invoke-Expression], ParseException
    + FullyQualifiedErrorId : InvalidVariableReferenceWithDrive,Microsoft.PowerShell.Commands.InvokeExpressionCommand