Fix IPython requirement

[alanhuang122]

IPython 6.0+ requires Python 3.3+, so only install that version if we're using Python 3.3+.

This fixes #1194.

[dgw]

Looks good, though the ipython module is actually excluded from tests so… lol.

That said, while this shouldn't hurt anything, I don't think it's actually necessary. Installing IPython with my local pip2 installed IPython 5.5.0, just as it should, because 6.x doesn't support py2. pip is generally smart enough to avoid installing incompatible package versions.

@alanhuang122 Can you think of a good reason to have these IPython requirements in requirements.txt, and also have IPython required in dev-requirements.txt? That just seems redundant. Pay no attention to the drowsy dgw behind the curtain.

[alanhuang122]

Yeah, I'd realized after opening this that builds were still succeeding even without this explicit specification. Not sure, in that case, what's going on with the issue.

There is no IPython requirement currently in requirements.txt, unless I'm blind.

[dgw]

You're not blind, I'm just GitHubbing tired (which one should never do, but I do anyway on a regular basis). It's not there. Which is strange, because it's a runtime dependency, not a dev dependency.

Maybe take this patch and put the requirement where it belongs, and remove it from dev-requirements?

At some point it might be worth considering making niche stuff like IPython (both the requirement and the module, if possible) only install if specifically requested using the extra requirements feature of python (e.g. you'd need to pip install sopel[with_ipython] to get it), but that's a bigger project.

[dgw]

🎉