Fixed typo in `Request` class docstring.

[jscanlo1]

Summary

Just a small typo in the docstring for the Request class. The content parameter is described as the content of the response body, rather than the request body.

Checklist

• [x] I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• [x] I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• [x] I've updated the documentation accordingly.

[karpetrosyan]

Thanks😊