Deprecated func fix rename fix

[elvismdev]

Description of the Change

• Closes create_new_site returning false - replaced insert_blog with wp_insert_site #95

How to test the Change

Run a single site to multisite import. No PHP deprecated warnings should output to the console. No PHP warnings when moving plugins and themes file assets.

Changelog Entry

Fixed - Deprecated WordPress function warning, insert_blog() with wp_insert_site().
Fixed - PHP warning when calling replace() - caused by PHP core bug https://bugs.php.net/bug.php?id=54097

Credits

Props @elvismdev

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests pass.