Update mocks for screenshots

[JavonDavis]

Updates the mocks for the app store screenshots

To test: Run screenshot tests

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

	Warnings
⚠️	PR has more than 500 lines of code changing. Consider splitting into smaller PRs if possible.

Generated by 🚫 dangerJS

[peril-wordpress-mobile]

You can test the changes on this Pull Request by downloading the APK here.

[designsimply]

I was able to get tests to work after updating to ddf3166! 🎉

The Discover screenshot looks amaaaazing. Yay! 😍

Nitpick: there's a gray overlay on the stats screen that isn't there when I browse with the app directly. Note that this may not matter if the overlay isn't present when generating screenshots at the fastlane level (I observed this in the test directly).

Nitpick: images in the media screenshot don't match the ones in the figma. This also might not matter but we could double check with Megs on the design if you want!