CI tasks for compiler are not running any tests
It seems that the current CI setup accidentally doesn't run any tests, while still displaying a "passing" state.

Looking at https://circleci.com/gh/kaitai-io/kaitai_struct_compiler/552, the step
> cat /dev/null | sbt test

exits with
```
[warn] No sbt.version set in project/build.properties, base directory: /home/circleci/repo
[info] Set current project to repo (in build file:/home/circleci/repo/)
[success] Total time: 3 s, completed May 11, 2020 10:08:51 AM
```

It doesn't seem to actually execute any tests.

On my local machine running `sbt test` results in

```
[info] Run completed in 2 seconds, 592 milliseconds.
[info] Total number of tests run: 1093
[info] Suites: completed 11, aborted 0
[info] Tests: succeeded 936, failed 157, canceled 0, ignored 0, pending 0
[info] *** 157 TESTS FAILED ***
[error] Failed tests:
[error]         io.kaitai.struct.exprlang.ExpressionsSpec
[error]         io.kaitai.struct.translators.TranslatorSpec
[error]         io.kaitai.struct.ErrorMessagesSpec
[error]         io.kaitai.struct.exprlang.Ast$Test
[error] (compilerJVM / Test / test) sbt.TestsFailedException: Tests unsuccessful
```