Bump pyxdg from 0.25 to 0.26

Bumps [pyxdg](https://github.com/takluyver/pyxdg) from 0.25 to 0.26.
- [Release notes](https://github.com/takluyver/pyxdg/releases)
- [Changelog](https://github.com/takluyver/pyxdg/blob/master/ChangeLog)
- [Commits](takluyver/pyxdg@rel-0.25...rel-0.26)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -89,7 +89,7 @@ python-apt==0.9.3.5ubuntu2
 python-dateutil==2.4.2
 python-debian==0.1.21-nmu2ubuntu2
 pytz==2015.7
-pyxdg==0.25
+pyxdg==0.26
 redis==2.10.5
 reportlab==3.0
 repoze.lru==0.6