Fix end-of-line character in ReferenceTest

ReferenceTest.java contains a bad end-of-line character (^M) that has side-effects in some 3rd-party tools (last line not displayed in [github blame page](https://github.com/EsotericSoftware/kryo/blame/master/test/com/esotericsoftware/kryo/ReferenceTest.java), SonarQube analysis fails, ...)