bump dependency pyyaml>=4.2b1

[ahmetb]

Otherwise any github project importing this package shows a high-severity security alert:

https://github.com/GoogleCloudPlatform/microservices-demo/blob/31df60f050a113c771a91477863ce93c8ed0f078/src/recommendationservice/requirements.txt#L30

[hrasadi]

Thanks for bringing this into our attention. We are working on fixing the dependencies and will soon release an update

[hrasadi]

Done with the release of agent version 2.10. We now use pyyaml 5.1.