Bump pytz from 2015.7 to 2019.2

Bumps [pytz](https://github.com/stub42/pytz) from 2015.7 to 2019.2.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](https://github.com/stub42/pytz/commits/release_2019.2)

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

requirements.txt

@@ -25,7 +25,7 @@ pycrypto==2.6.1
 paramiko==1.16.0
 pyasn1==0.1.9
 pycparser==2.14
-pytz==2015.7
+pytz==2019.2
 sqlparse==0.1.16
 static3==0.6.1
 Fabric==1.14.0