chore: update ios/android versions

- update iOS version on Sauce Labs because iOS 10 has been deprecated
- add Android 8.1 for native and ChromeDriver screenshot
- added breaking change by removing `ignoreTransparentPixel`
- already update `webdriver-image-comparison` to latest version

CHANGES.md

@@ -4,6 +4,7 @@
 - create a `canvasScreenshot` of an element has been removed
 - `saveFullPageScreens` has been renamed to `saveFullPageScreen`
 - `nativeWebScreenshot` has been removed from the options. This can only be added/determined from the capabilities
+- `ignoreTransparentPixel` has been removed from the options.
 - `androidOffsets` and `iosOffsets` have been removed from the options. They are now set for a lot of iOS and Android versions in the [`webdriver-image-comparison constants.ts`](https://github.com/wswebcreation/webdriver-image-comparison/blob/master/lib/helpers/constants.ts)
 - dropped support for Firefox 47
 - dropped support for Safari 9