Fix version number

[Archmonger]

Description

Fix accidental version revert on reactpy, and update changelog to indicate new version release

Checklist:

Please update this checklist as you complete each item:

• [x] Tests have been included for all bug fixes or added functionality.
• [x] The changelog has been updated with any significant changes, if necessary.
• [x] GitHub Issues which may be closed by this PR have been linked.

[Archmonger]

I think we might also want to remove the accidental v3.0.0a4 on pypi