Empty Stats: update grow audience ghost cell layout

[momo-ozawa]

Description

This PR updates the grow audience ghost cell layout.

Ref: #17142 (comment)

Before	After

How to test

1. Delete app and do a fresh install
2. Go to My Site > Stats
3. ✅ Notice that the ghost loading layer matches the new design specs

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• 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 an installable build for these changes by visiting CircleCI here.

[peril-wordpress-mobile]

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

[osullivanchris]

Looks good to me! @leandroalonso does this resolve the concern you had on it?

[leandroalonso]

@osullivanchris yep yep