Comply with POSIX

All Linux and Mac systems have `hostname`, but `uname -n` will continue working if PowerShell is released on other POSIX systems.

Author: pavelbraginskiy

Helpers/Prompt.ps1

@@ -38,7 +38,7 @@ function Get-ComputerName {
         if ($env:NAME) {
             return $env:NAME
         } else {
-            return (hostname)
+            return (uname -n)
         }
     }
     return $env:COMPUTERNAME