Extend CI test matrix about elixir_sense

[lukaszsamson]

CI now runs tests on elixir 1.7-1.10 and otp 19-22. I made it not required to pass all tests on < 1.9. It does not give a full certainty but at least we can see if the code is not terribly broken.

[lukaszsamson]

#91 has to be addressed first

[axelson]

I agree that this would be a good change

[msaraiva]

Would it be a good idea to start moving only the failing tests on 1.10.1? And then on every new version, if we have more tests failing, we address them individually until we get all (most) of them done. I mean, I'm not sure yet how long it would take to address all of them at once.