Import cycles not reported

[tfausak]

If there is an import cycle, Purple Yolk stops doing anything interesting and doesn't report the error. The output from GHCi looks like this:

2020-06-11T15:21:07.527Z [ghci/stdout] {"span": null,"doc": "Module imports form a cycle:\n  module `Example' (.../Example.hs) imports itself","severity": "SevFatal","reason": null}

I think no spans are included because cycles may involve arbitrarily many modules.

[tfausak]

This was kind of accidentally addressed by #16:

Unfortunately it's (a) not associated with any particular file and (b) reported as "info" rather than "error". But at least it's reported!