#145 - Native function type declarations

[krzysztofkozyra021]

This should close #145

Before:

<?php

declare(strict_types=1);

enum Status: String
{
    case Active = "active";
}

enum Priority: Int
{
    case High = 1;
}

After:

<?php

declare(strict_types=1);

enum Status: string
{
    case Active = "active";
}

enum Priority: int
{
    case High = 1;
}

PHP does not recognize String or Int as valid scalar types; only lowercase string and int are allowed.