Update Guard.cs

src/ImageSharp/Common/Helpers/Guard.cs

@@ -2,9 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-#if NETSTANDARD1_3
-using System.Reflection;
-#endif
 using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp;
 
@@ -22,11 +19,7 @@ namespace SixLabors
         [MethodImpl(InliningOptions.ShortMethod)]
         public static void MustBeValueType<TValue>(TValue value, string parameterName)
         {
-            if (value.GetType()
+            if (value.GetType().IsValueType)
-#if NETSTANDARD1_3
-                .GetTypeInfo()
-#endif
-                .IsValueType)
             {
                 return;
             }