Add "Diagnostic" to ValidateSet for LogLevel

Author: kamilkosek

module/Start-EditorServices.ps1

@@ -44,7 +44,7 @@ param(
     [ValidateNotNullOrEmpty()]
     $LogPath,
 
-    [ValidateSet("Normal", "Verbose", "Error")]
+    [ValidateSet("Normal", "Verbose", "Error","Diagnostic")]
     $LogLevel,
 
     [switch]
@@ -191,4 +191,4 @@ catch [System.Exception] {
     }
 
     Write-Error ("`r`nCaught error while waiting for EditorServicesHost to complete:`r`n" + $errorString)
-}
+}