Option are displayed in lowercase in help

**Describe the bug**
When no long or short name is provided for an option, the help display this option in lowercase

**To Reproduce**
Run this console program adding in the command line "--help "

```
class Options
{
[Option(HelpText = "Specify the input file.")]
public string InputFile { get; set; }
}

class Program
{
static void Main(string[] args)
{
var result = Parser.Default.ParseArguments(args);
result.WithParsed(options =>
{
Console.WriteLine($"InputFile: {options.InputFile}");
})
.WithNotParsed(errors =>
{
});
}
}
```

**Expected behavior**
"InputFile" instead of "inputfile"

**Screenshots**

**Additional context**
I saw that it's in Specification.cs class method FromProperty that there is a call to ToLowerInvariant() that make the display lower