M2 Version 4.2.0 release

[cykolln]

Description

• Update the Magento 2 klaviyo.js url to the new format
• bumps version
• small fix for Area code is already set bug (Area code is already set  #166, Area Code is already set. #296)

Manual Testing Steps

1. tested on local site - made sure that form appears and the url is formatted correctly.
   

Pre-Submission Checklist:

• You've updated the CHANGELOG following the steps here
• Internal Only - If this is a release, please confirm the following:
  • The links in the changelog have been updated to point towards the new versions
  • The version has been incremented in the following places: module.xml and composer.json

NOTE: Please use the Changelogger cli tool to manage versioned file upgrades.