Update assertj+tests work with other locales

[asturio]

Dependencies updated:

• maven-assembly-plugin 3.0.0 -> 3.2.0 (bogus warning)
• assert 2.9.0 -> 3.15.0

AssertJ Unittests run on other locales

• Some Tests expect Messages in english, and running them on other locales
  won't work. So the test-classes set the locale to english before the tests
  and restore them after the tests

[coveralls]

Coverage increased (+0.7%) to 92.461% when pulling f5f77fd on asturio:update-assertj+tests-work-with-other-locales into 4866621 on xmlunit:master.

[bodewig]

Many thanks @asturio .

This module depends on AssertJ 2.x in order to be buildable with Java7 - see https://travis-ci.org/github/xmlunit/xmlunit/jobs/675025927. I don't think your changes really require us updating the dependency. Could you please revert that part?

Also please add a license header to the new LocaleModifier file.

What you are doing with LocaleModifier and Before/AfterClass looks like a candidate for a JUnit TestRule annotated with ClassRule to me.

[bodewig]

After re-installing my OS I'm now facing the same problem :-)

I've decided to take a slightly different approach, though. See c5f1899

Many thanks!