chore(deps): update dependency pytz to v2019.3 [(#3190)](GoogleCloudPlatform/python-docs-samples#3190)

Co-authored-by: Leah E. Cole <[email protected]>

Author: 2 people

samples/snippets/requirements.txt

@@ -2,4 +2,4 @@ google-cloud-bigquery[pandas]==1.20.0
 google-auth-oauthlib==0.4.0
 ipython==7.8.0
 matplotlib==3.1.1
-pytz==2019.2
+pytz==2019.3