Invalid getMimeType for audio/mp3

### Code

```php

use DataURI\Parser;

$audio = Parser::parse('data:audio/mp3;base64,SUQzBAAAAAAAI1RTU0UAAAAPAA');
$mime = $audio->getMimeType();
echo $mime;
```

### Expected
```
audio/mp3
```

### Output
```
audio/mp
```