Update urwid from 2.6.4 to 2.6.8: fixed known bugs and regressions

[Aleksei Stepanov]

Urwid 2.6.8 contains fixes for known issues and potential crashes:

* Allow wcwidth to select unicode version (allow to force via environment variables, unlock prehistoric wcwidth support)
* Special case: in case of Columns/Pile empty - use fallback sizing (was render problems with gerrit client)
* Always support FLOW for Columns sizing if not BOX-only (was render problems with gerrit client)
* Fix rows method for Columns in case of FIXED only widgets present (was crash on pack call, while render worked correctly)
* Columns: pack and render should produce the same size if some widgets skipped (very old bug causes incorrect rows calculation in case of columns with weight=0 present)
* Fix MainLoop.watch_pipe regression for the callback outcome not False
* Fix regression: Overlay not accepted relative positioning

[Aleksei Stepanov (penguinolog)]

Package is updated (checked)