Fix exception message for wrong response type

[MarSoft]

Looks like this fork is alive, unlike the upstream repo.

[MarSoft]

@nugend, did you consider publishing this fork on pypi as e.g. nugend-qpython? This would greatly simplify using qpython on python3.7.
Or I could do it myself based on your fork.

[nugend]

https://github.com/gusutabopb/qPython3 Is also working on a fork.

I needed to build this fork for my own purposes but cannot currently support it meaningfully.

Thanks for the patch though!