switch to Java 8

Just a heads up that the build system (https://adams.cms.waikato.ac.nz/jenkins/) has switched to Java 8. Some reference files for the regression tests needed to be updated during that process.

Currently, the code base is still Java 7 and it still compiles to 7. However, this might change in the future without further notice.

Why? Java 7 will reach its end-of-life in April this year.