Update dependency google-cloud-pubsub to v1.4.2 [(#3340)](GoogleCloud…

…Platform/python-docs-samples#3340)

Co-authored-by: Leah E. Cole <6719667+leahecole@users.noreply.github.com>

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

@@ -1,4 +1,4 @@
-google-cloud-pubsub==1.0.0
+google-cloud-pubsub==1.4.2
 google-cloud-containeranalysis==0.3.1
 grafeas==0.1.0
 pytest==5.3.0; python_version > "3.0"