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

@@ -45,7 +45,7 @@ pytest==4.4.1
 python-dateutil==2.7.5
 pytz==2018.7
 pyverdict==0.1.3.2
-pyxdg==0.25
+pyxdg==0.26
 PyYAML==3.12
 requests==2.18.4
 scikit-learn==0.20.3