Bump up JUnit version to 5

[npathai]

Presently JUnit 5 is under alpha stage, once it is open for public use we should update library.

JUnit 5 is lambda ready and provides variety of features pre-built that will remove some library dependencies.

Plus it never hurts to stay updated and we can provide feedback on any broken features.

[iluwatar]

It should be quite stable already http://junit.org/junit5/. Also, it should be straightforward to run JUnit4 and JUnit5 test cases side by side, so migration can be gradual.

[amogozov]

@iluwatar I would like to give it a try!

[iluwatar]

Ok @amogozov