Issue #123 update grpc to version 1.24 protoc to version 3.9.1

[lt-schmidt-jr]

update grpc to version 1.24
update protoc to version 3.9.1
small changes to fix API changes and test

[salesforce-cla]

Thanks for the contribution! Unfortunately we can't verify the commit author(s): Kogan, Mike <m***@i***.com>. One possible solution is to add that email to your GitHub account. Alternatively you can change your commits to another email and force push the change. After getting your commits associated with your GitHub account, sign the Salesforce.com Contributor License Agreement and this Pull Request will be revalidated.

[lt-schmidt-jr]

added #124
NOTE that there is an issue with Guava dependency in contrib.spring. Let me know if you would like me to try to help with it. I can also make a PR to another branch