add parens in error msg

Author: mythz

src/ServiceStack.Text/DynamicNumber.cs

@@ -450,8 +450,8 @@ public static IDynamicNumber AssertNumbers(string name, object lhs, object rhs)
             if (number == null)
             {
                 throw new ArgumentException($"Invalid numbers passed to {name}: " +
-                                            $"{lhs?.GetType().Name ?? "null"} '{lhs?.ToString().SubstringWithElipsis(0, 100)}', " +
-                                            $"{rhs?.GetType().Name ?? "null"} '{rhs?.ToString().SubstringWithElipsis(0, 100)}'");
+                                            $"({lhs?.GetType().Name ?? "null"} '{lhs?.ToString().SubstringWithElipsis(0, 100)}', " +
+                                            $"{rhs?.GetType().Name ?? "null"} '{rhs?.ToString().SubstringWithElipsis(0, 100)}')");
             }
 
             return number;