Verify and update WordPress 5.4 compatibility

[ahmadbilaldev]

Fixes #98

Description

I have made sure everything is up to date and works. All the changes mentioned do not essentially require any changes so far. This PR also updates the "Tested up to" field in readme to 5.4.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the master branch of the repository.
• My commit messages follow best practices.
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[kgodey]

Thanks @ahmadbilaldev!

[hugosolar]

Hey Ahmad
I'm getting deprecated notifications in the browser console, I think is due to a change on the blocks API made in 5.4 (I couldn't find that information)

Maybe if you change the const value on the blocks JS files it should work.

[ahmadbilaldev]

Hi Hugo,
I'll give it a check.

[hugosolar]

Ok, this is fixed in #105