Migration from MSDN missed a spot (#4318)

* Add a missing ms.assetid

* Actually fix that link

* Update installing-the-windows-powershell-sdk.md

Author: SamB

developer/windows-powershell.md

@@ -21,7 +21,7 @@ Windows PowerShell .
 
 ## Windows PowerShell Documents on MSDN
 
-- [Installing the Windows PowerShell SDK](https://msdn.microsoft.com/en-us/library/ff458115.aspx)
+- [Installing the Windows PowerShell SDK](./installing-the-windows-powershell-sdk.md)
 Provides information about how to install the Windows PowerShell SDK.
 
 - [Writing a Windows PowerShell Module](./module/writing-a-windows-powershell-module.md)