chore(deps): update dependency click to v8 (GoogleCloudPlatform#877)

Author: renovate-bot

src/loadgenerator/requirements.txt

@@ -12,7 +12,7 @@ certifi==2020.12.5
     #   requests
 charset-normalizer==2.0.10
     # via requests
-click==7.1.2
+click==8.1.3
     # via flask
 configargparse==1.5.3
     # via locust