Make sure amp styles work with logo centering

[laurelfulford]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

There is a weird case where AMP will add the following CSS to a site, and it will cause the centred logo not to work when they have a width, height and sizes attribute:

[width][height][sizes]:not(.i-amphtml-layout-responsive) {
    display: block;
    position: relative;
}

This PR adds some 'backup' CSS in this cases, so rather than relying on the img to be display: inline-block, it will also work when it's display block.

How to test the changes in this Pull Request:

1. Test on a site that's displaying this issue.
2. Confirm that the logo is not centring.
3. Apply the PR and run npm run build.
4. Confirm that it fixes the issue.
5. If possible, test on a site that is not displaying this issue on master and confirm that it doesn't cause any issues.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

[jeffersonrabb]

Here are the conditions to replicate the issue:

• AMP transitional mode
• Center Logo theme mod
• Newpack Pop-ups installed

Newspack Pop-ups enqueues various AMP scripts even if the request is non-AMP, which is probably the cause of the issue.

[jeffersonrabb]

Fix works great.

[laurelfulford]

Thanks Jeff!

[matticbot]

🎉 This PR is included in version 1.6.1 🎉

The release is available on GitHub release

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