Change 'App signing' to 'App integrity' (#65)

[HarshKapadia2]

Fixes #65

PR Type

• Refactoring (no functional changes, no api changes)
• Documentation content changes

Describe the current behavior?

From a comment in issue #65:

In the Next-steps.md file, the 4th step ('Update your asset links file for production') requires the developer to choose Setup -> App signing in the Google Play Console and then copy their SHA-256 fingerprint from there. The name in the nav bar on the left of the page has now changed to 'App integrity' (as shown in the picture below), so there should be a correction from Setup -> App signing to Setup -> App integrity.

The same applies to the 'Add production fingerprint' section in the Asset-links.md file.

Describe the new behavior?

Changes mentioned in issue #65.

• The target text in Next-steps.md and Asset-links.md has been changed to Setup -> App integrity.
• The old image has been replaced with the new UI of the Google Play Console.

PR Checklist

• [ ] Test: run npm run test and ensure that all tests pass
• [x] Target master branch (or an appropriate release branch if appropriate for a bug fix)
• [ ] Ensure that your contribution follows standard accessibility guidelines. Use tools like https://webhint.io/ to validate your changes.

[ghost]

Thanks HarshKapadia2 for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌

[ghost]

All CLA requirements met.