junit-vintage-engine as runtimeOnly dependency

[realdadfish]

I discovered some quirks in my setup when I added the dispatch-test artifact to my test classpath. This artifact transitively pulls org.junit.vintage:junit-vintage-engine into the test compile classpath, which - by documentation - should only reside in the test runtime's classpath (i.e. testRuntimeOnly). The quirk now was that when I added dispatch-test, my tests were executed as wanted (as the JUnit4 runtime was on the classpath), but as soon as I removed it, tests weren't executed anymore.

The solution for me was obviously to depend on junit-vintage-engine myself, but I thought it might be a good idea to get rid of it in the transitive classpath as well.

[RBusarow]

Thanks for the report! I'll get this fixed tonight.