Tests for cross Scala versions

[lastland]

Now we have cross build for Forklift. Unfortunately, there is no cross test. The reason is that part of Forklift's test is copying an example Scala project and run tests against it. The example project has its own build definition, thus a +test in Forklift will not be able to test different versions of the example project.

The solution I have in mind is to utilize parallelization in CircleCI. We need to have a script to change the Scala version in the build definition of the example project. Then on one specific machine, the script is executed before running tests.