Update dependency google-cloud-containeranalysis to v0.3.1 [(#3055)](GoogleCloudPlatform/python-docs-samples#3055)

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

Author: 2 people

samples/snippets/requirements.txt

@@ -1,5 +1,5 @@
 google-cloud-pubsub==1.0.0
-google-cloud-containeranalysis==0.3.0
+google-cloud-containeranalysis==0.3.1
 grafeas==0.1.0
 pytest==5.3.0; python_version > "3.0"
 pytest==4.6.6; python_version < "3.0"