add missing using statement

Author: bergmeister

Engine/Commands/InvokeFormatterCommand.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+using Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic;
 using System;
 using System.Globalization;
 using System.Management.Automation;