Disabled ghost button isn't... ghosted

## 🐛 Bug Report

When disabled, a `Submit` doesn't appear as expected.

## To Reproduce

Steps to reproduce the behavior:
- `Submit`

## Expected behavior

It is not clear anywhere how to override this and I would expect the button to show adjust grey text without a background or border.

## Link to runnable example or repository (highly encouraged)

https://snack.expo.dev/GDCG5X4Hj

## UI Kitten and Eva version

| Package | Version |
| ----------- | ----------- |
| @eva-design/eva | 2.0.0 |
| @ui-kitten/components | 5.0.0 |

## Environment information

```
System:
OS: macOS 11.5.2
CPU: (4) x64 Intel(R) Core(TM) i7-5557U CPU @ 3.10GHz
Binaries:
Node: 16.7.0 - /usr/local/bin/node
Yarn: 1.22.10 - ~/Bundu/mobile-app/node_modules/.bin/yarn
npm: 7.20.3 - /usr/local/bin/npm
Watchman: 2021.08.02.00 - /usr/local/bin/watchman
SDKs:
iOS SDK:
Platforms: iOS 14.5, DriverKit 20.4, macOS 11.3, tvOS 14.5, watchOS 7.4
IDEs:
Xcode: 12.5.1/12E507 - /usr/bin/xcodebuild
npmPackages:
react: 16.13.1 => 16.13.1
react-native: 0.63.4 => 0.63.4
```