Sbt 1.4.8 minimal fix

[note]

I don't know basically anything about either sbt-plugins or sbt-errors-summary in particular. I was mostly following error messages. I published it locally and tested it manually with following sbt versions: 1.1.4, 1.2.4, 1.3.7, 1.4.2 and 1.4.9. I used scala 2.13 in all those project. It looks that fix worked for those projects, I will keep on using my locally published version for some time.

The first commit of this PR alone is enough to fix the issue. The other ones are attempts to fix CI build but I have not managed to make tests pass for any scala version besides 2.12. My gut feeling though is that it's rather about how tests are run. It seems that in CompilerSpec compiler.compile ends up using scala lib 2.12 regardless which scala version we target. I gave up on fixing that, I think someone more versed with sbt would need to take a look. Also, the fact that the project hasn't been updated for a quite while does not make it easier

[Duhemm]

Thanks a lot @note ! I'll take a look as soon as possible.

It looks like CI wasn't run on this PR (doesn't show any check)? Do you know why that is?

[note]

@Duhemm It took me some time to realize that actually it was run on the CI, here is the link: https://travis-ci.org/github/Duhemm/sbt-errors-summary/builds/762747964

I am not 100% sure why check doesn't show up in the PR but I guess it has something to do with either travis-ci.org -> travis-ci.com move or with your account's settings. At some moment I had to add additional permissions in https://github.com/settings/installations. Right now I have Travis CIas Installed Github Apps and also Travis CIand Travis CI for Open Source in Autorized Auth Apps. It was always confusing to me, I don't know which one is effective.

Anyway, Travis changed their policy and it doesn't make much sense to use it for OSS on the long run. You can consider moving to github-actions. I can prepare a PR in a few days, I just did it for some projects yesterday

[Duhemm]

Thanks a lot @note 🎉 ! I fixed the conflicts and kept the minimal fix from your branch.