build on Java 11

[mattnworb]

We should start building Helios on Java 11 in CI.

This seems like it will be somewhat of a headache, or at least not possible today. We use the "machine"-based builds in CircleCI which at time of writing run on Ubuntu 14.04 which only has Java 8 available.

https://circleci.com/docs/2.0/executor-types/#using-machine mentions it is possible to specify the image of the "machine" to be used, but it looks to me like all of them have the same OS/distribution.

See also https://discuss.circleci.com/t/image-with-oracles-java-10/23220

I don't have a solution in mind yet but am opening this to track it at least.

[mattnworb]

will need to bump docker-client to 8.14.0 to make it Java 9+ compatible

[davidxia]

WIP here #1242