[screengrab] fix formatting of the screengrab / capture_android_screenshots docs

[AliSoftware]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I see several green ci/circleci builds in the "All checks have passed" section of my PR (connect CircleCI to GitHub if not)
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

The generated HTML for this page renders some of the code blocks incorrectly.

Description

Hopefully, by adding newlines before those code blocks it will fix the issue in the HTML generated by mkdocs.

Testing Steps

Warning: I did NOT run mkdocs on the resulting file to check that it actually solves the issue on the generated HTML (as I don't have mkdocs installed and I'm a bit short on time today to install it).

A reviewer could try to do that first though, to confirm the changes in this PR fix the formatting issue.

[joshdholtz]

Going to just merge this to see if this fixes this issue because I like how this looks in the markdown anyway 😊