An error occurs when parsing code that uses traits.

v0.3.0

An error occurs when loading a trait.

```
PHP Fatal error:  Uncaught TypeError: Cannot assign PhpParser\Node\Stmt\Trait_ to property Smeghead\PhpClassDiagram\Php\PhpClass::$syntax of type PhpParser\Node\Stmt\Class_|PhpParser\Node\Stmt\Interface_
```

Loading a file with traits defined shouldn't cause an error.