Issue in /src/pages/ps_reference/classes/layer.md

The example code for the `flip` method is incorrect. The signature says it requires the `axis` parameter but the example code shows calling an `axis` method on the `flip` method.

**Current (Incorrect) Example**

```javascript
// flip horizontally
await layer.flip.horizontal()
```

**Corrected Example**

```javascript
// flip horizontally
await layer.flip("horizontal")
```