DTD tests always fail on Travis

[sonofmun]

Example: https://travis-ci.org/OpenGreekAndLatin/First1KGreek/builds/276773069
This is because Travis has started printing out the line "Picked up _JAVA_OPTIONS: -Xmx2048m -Xms512m" whenever jing.jar is run (see, e.g., rspec/rspec-dev#185)

[sonofmun]

This solution still needs a unit test written for it. Perhaps a Mock of a subprocess?