Include invalid JSON body in ParseErrors

[hermo]

The docs state that a ParseError includes a response as does HTTPError, for example.

A HTTPError includes response.body and PR makes ParseError behave similarly by including the invalid "JSON" in response.body. This is useful for error handling and debugging than the the SyntaxError: Unexpected token / in JSON at position 0 in the actual error message.

Checklist

• I have read the documentation.
• I have included a pull request description of my changes.
• I have included some tests.

[szmarczak]

Good job 🎉