Java: roman-numerals: update version file and add test (1.0.0 -> 1.2.0)

[FridaTveit]

Please update the version specified in the roman-numerals version file from 1.0.0 to 1.2.0.

Please also include one extra test which is included in the canonical data but not in our tests; between the tests for converting 48 and converting 59 there should be a test for converting 49.

Background info: each exercise which has canonical data should have a version file. This file states which version of the canonical data the exercise implements. The version can be found at the top of the canonical data file for that exercise.

[katmpatz]

@FridaTveit, if this issue is already open I would really want to contribute!

[sjwarner-bp]

Feel free to pick this one up @katmpatz ! :slightly_smiling_face:

[FridaTveit]

Yes, go for it @katmpatz 🙂