Bump our minimum supported version of WordPress to 5.5

[dkotter]

Description of the Change

While prepping for the 1.0.5 release I realized our E2E tests were failing on WP 5.4, which was our minimum supported version. This was due to changes introduced in #130 that rely on a certain HTML structure. In discussion there, it was determined to bump our minimum version up to where those changes were introduced in WP, which is 5.5.

Alternate Designs

Could fix the JS introduced in #130 to work on 5.4

Possible Drawbacks

Any user's running on WP 5.4 won't be able to update

Verification Process

Verify the WP Minimum E2E test passes (the other two are failing due to timeouts, which seems to have been the case for a bit)

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

Changed - Bump our minimum supported WordPress version to 5.5

Credits

Props @dkotter, @jeffpaul, @peterwilsoncc

[peterwilsoncc]

I've pushed aec08e5 to fix some linting errors.

Some of the E2E jobs are failing on the front end assertion cy.contains( 'Hello world∀' ); but I am unable to figure out why as Docker broke itself during a recent update.

[peterwilsoncc]

Change looks good, approving and merging as the tests are broken on the main branch.