chore(deps): update dependency pytz to v2020 (#3566)

Author: renovate-bot

bigquery/cloud-client/requirements.txt

@@ -2,4 +2,4 @@ google-cloud-bigquery[pandas]==1.24.0
 google-auth-oauthlib==0.4.1
 ipython==7.13.0
 matplotlib==3.2.1
-pytz==2019.3
+pytz==2020.1