Merge pull request #103 from natsu1211/fix-nested-exception-message

Fix message of NestedStringBuilderCreationException throwed by Utf8ValueStringBuilder.ThrowNestedException()

src/ZString/Utf8ValueStringBuilder.cs

@@ -402,7 +402,7 @@ void ThrowFormatException()
 
         static void ThrowNestedException()
         {
-            throw new NestedStringBuilderCreationException(nameof(Utf16ValueStringBuilder));
+            throw new NestedStringBuilderCreationException(nameof(Utf8ValueStringBuilder));
         }
 
         private void AppendFormatInternal<T>(T arg, int width, StandardFormat format, string argName)