Bump pytz from 2018.9 to 2019.1

Bumps [pytz](https://github.com/stub42/pytz) from 2018.9 to 2019.1.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](stub42/pytz@release_2018.9...release_2019.1)

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

requirements.txt

@@ -96,7 +96,7 @@ inflection<=0.3.1
 jdcal==1.4
 mock<=2.0.0
 python-dateutil==2.8.0
-pytz==2018.9
+pytz==2019.1
 requests==2.22.0
 simplejson==3.16.0
 timeout-decorator==0.4.1