Documentation corrections for AvoidUsingPositionalParameters

[God-damnit-all]

This is just a minor PR for fixing a couple of typos in the documentation.

Rules = @{
-    AvoidUsingPositionalParameters = @{
+    PSAvoidUsingPositionalParameters = @{
        CommandAllowList = 'az', 'Join-Path'
        Enable           = $true
    }
}

- #### AvoidUsingPositionalParameters: string[] (Default value is 'az')
+ #### CommandAllowList: string[] (Default value is 'az')

[bergmeister]

Thanks, good catch. @sdwheeler It would be great to sync those fixes to the Docs repo since they apply to already published version of PSSA, I created this PR here: bergmeister/PowerShell-Docs-Modules#2