Replace convertkit.com with kit.com

[n7studios]

Summary

Replaces convertkit.com with kit.com

Testing

Existing tests pass

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)

[n7studios]

@noelherrick There's still 4 lines in the tests that need to reference convertkit.com:

Fetching Legacy Landing Pages via the API:

https://api.convertkit.com/v4/landing_pages?type=hosted
{
    "legacy_landing_pages": [
        {
            "id": 470103,
            "name": "Legacy Landing Page",
            "created_at": null,
            "type": "hosted",
            "url": "https://app.convertkit.com/landing_pages/470103",
            "embed_js": "https://api.convertkit.com/api/v3/forms/470103.js?api_key={apikey}",
            "embed_url": "https://api.convertkit.com/api/v3/forms/470103.html?api_key={apikey}",
            "title": "",
            "description": "",
            "sign_up_button_text": "Register",
            "success_message": null,
            "archived": false
        }
    ],
    ...
}

Fetching HTML for a legacy form e.g https://api.kit.com/forms/470099/embed?v=2&k={apikey}

• The form HTML in the returned legacy form is <form id="ck_subscribe_form" class="ck_subscribe_form" action="https://api.convertkit.com/landing_pages/470099/subscribe" data-remote="true">

Fetching HTML for a landing page e.g. https://cheerful-architect-3237.ck.page/99f1db6843

• The form HTML in the returned hosted landing page is <form method="POST" action="https://app.convertkit.com/forms/2765196/subscriptions"

Fetching HTML for a landing page e.g. https://cheerful-architect-3237.ck.page/cc5eb21744

• The form HTML in the returned hosted landing page is <form method="POST" action="<form method="POST" action="https://app.convertkit.com/forms/2849151/subscriptions""

Would the <form> URLs change once the switch is fully made to kit.com from convertkit.com?

[noelherrick]

@n7studios That's correct - all URLs will change, including *.ck.page URLs. Those will now be hosted on *.kit.com

[n7studios]

@n7studios That's correct - all URLs will change, including *.ck.page URLs. Those will now be hosted on *.kit.com

Okay, great - I'll submit a PR with amended tests once the URLs change to *.kit.com. Thanks!