Fix to use a synchronous assertion

[trknhr]

Hi

I found a snippet that I want to fix.
Although It set the asynchronous flag as false, errors were called in asynchronous events. This throw error cannot be detected by Autify because it detects only synchronous errors.

When this flag is set as false, xhr.send blocks later processes until receiving the server's response.
https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/Synchronous_and_Asynchronous_Requests#example_http_synchronous_request

Please check it. Thank you.

[meih]

@trknhr
Thank you for your suggestion!
You will be the first-time contributor to this repo from outside Autify 🎉

At the same time, we care about your contribution in terms of your rights.
Upon merging, do you agree to allow other users to use the updated snippet?

Thank you!

[trknhr]

@meih Thank you for your reply. There is no problem that other users use it.

[meih]

Thank you! Your PR will be reviewed soon.