fixup! UnitSystem: R# cleanup

Author: angularsen

UnitsNet/CustomCode/UnitSystem.cs

@@ -23,6 +23,7 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using System.Reflection;
 using JetBrains.Annotations;
 using UnitsNet.I18n;