- Update to 2.8.1:
* Fix rst file formats and links #229
* Add .gitattributes for generated and documentation files
* Add more complete tox and Travis envs with many checks
* Fix removing message format argument
* Fix QGroupBox small indicator size #218
* Fix QGroupBox incorrect indicator icon when unfocused #219
* Fix QDateTimeEdit incorrect drop-down arrow icon #220
* Fix documentation

- Rename dependency xorg-x11-server-Xvfb to xorg-x11-Xvfb, since
the former is not available in SLE/Leap and the later is provided
in both.