No example usage for render custom day in Official React Native UI Kitten Page

## 💬 Question
I have already check this site [React Native UI Kitten](https://akveo.github.io/react-native-ui-kitten/docs/components/calendar/overview)

Then scroll to section.
```To render custom cells, renderDay, renderMonth and renderYear properties may be used.```

but the example code is wrong, the site show how to render renderArrowLeft or renderArrowRight.

Can you update and fix it.

## UI Kitten and Eva version

| Package | Version |
| ----------- | ----------- |
| @eva-design/eva | 2.2.0 |
| @ui-kitten/components | 5.3.1 |