Update dependency google-cloud-pubsub to v1.4.2 in functions and IoT [(#3342)](GoogleCloudPlatform/python-docs-samples#3342)

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

Author: busunkim96

samples/api-client/manager/requirements.txt

@@ -4,6 +4,6 @@ google-api-python-client==1.8.0
 google-auth-httplib2==0.0.3
 google-auth==1.14.0
 google-cloud-iot==1.0.0
-google-cloud-pubsub==1.1.0
+google-cloud-pubsub==1.4.2
 paho-mqtt==1.5.0
 pyjwt==1.7.1