Fix: Using callback approach so attachments param can be included

[cahirodoherty-learningpool]

Fixes: #117

Fix

• sendStatement calls which include attachments will now work as expected

Testing

Create a course with xapi extension and a custom plugin that will add an 'attachments' array of objects to the xapi statement. Attachment objects should be of the form outlined here - https://www.npmjs.com/package/xapiwrapper/v/1.11.0#send-statement-with-attachments

[github-actions[bot]]

:tada: This PR is included in version 1.1.3 :tada:

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