Move Dart language to a different bucket of E2E tests on Travis

[izeigerman]

Although the Dart has been configured in .travis.yaml I don't see it's being executed. Eg. recent master build - https://travis-ci.org/BayesWitnesses/m2cgen/jobs/660185796.
Error in the output:

Unknown pytest.mark.dart - is this a typo?  You can register custom marks to avoid this warning

CC: @StrikerRUS

[izeigerman]

Additionally it seems like it's not a great idea to put Dart into the same bucket as R, since R tests already take 24 minutes, while other buckets take only ~4 and 8.5 minutes to complete.

[izeigerman]

Oops, sorry, I've just noticed that it's there for PR builds. We should still move it to a different bucket though.

[StrikerRUS]

I'm looking into master jobs: https://travis-ci.org/BayesWitnesses/m2cgen/builds/660185788.
In all buckets only the first language tests are run (c_lang, c_sharp, r_lang).

UPD: pytest issue?..

UPD2: rerunning all Python 3.7 tests in master...

UPD3: during re-running Python 3.7 tests everything seems to be OK - all language tests are executed now.

UPD4: Hope it was a random pytest error. I'm going to update branch in #176 right now. Let's take a look at those builds.

[StrikerRUS]

Sorry, wrong button. Seems that PR builds are OK. Re-running the rest of master incomplete builds.

[izeigerman]

Hm, yeah. Super weird. Thanks for looking into this!

[StrikerRUS]

Yes, indeed...

[izeigerman]

Seems not to be an issue. Closing this for now.