``RoutePartitionerTokeniserTest`` can now be run headless-ly

``Util.defaultLineSeparator`` requires loading some UI class, and that is a
problem because our CI server can only build headless-ly. The fix was simple,
just use ``\n`` in testing code.

The failure was introduced in SHA: 6b796dbde3547b0bf445aa19a30b37998c74d16d