Update term/taxonomy import

[kevmarsden]

Updates the term/taxonomy import functionality to make it compatible with Statamic 5.

The primary changes are:

• Replaces $taxonomy->set($key, $value); with Taxonomy::make
• Fixing the exists check in the WpImporter.php file

Closes #9

[jackmcdade]

Thanks! @kevmarsden do you happen to have a dummy import file I could use for testing?

[kevmarsden]

@jackmcdade attached is an export file with faker data. Let me know if you see any issues.

statamic_faker_export.json

[jackmcdade]

Perfect, thank you!