chore(deps): update dependency pyarrow to v4 (#641)

Author: renovate-bot

packages/google-cloud-bigquery/samples/snippets/requirements.txt

@@ -8,5 +8,5 @@ matplotlib==3.3.4; python_version < '3.7'
 matplotlib==3.4.1; python_version >= '3.7'
 pandas==1.1.5; python_version < '3.7'
 pandas==1.2.0; python_version >= '3.7'
-pyarrow==3.0.0
+pyarrow==4.0.0
 pytz==2021.1