Fix typo in fetching XHR url for breadcrumbs

[Hamish-taylor]

This bug fixes a typo in the breadcrumbs code when it try's to fetch the URL for a failed request.

This bug was raised in https://github.com/MindscapeHQ/raygun4js/issues/508.

https://github.com/MindscapeHQ/raygun4js/blob/fe73f53dd0af9dd8002025eb6fdd13238eb01de9/src/raygun.breadcrumbs.js#L478

error.requestUrl should be error.requestURL

Before

After

[PanosNB]

I'm happy for this to go to production. Small change and was tested in prerelease on our website