Update from javaslang to io.vavr

[sjudeng]

The pending CQL backend (#166) adds the javaslang dependency. This should be updated to the new io.vavr coordinates.

[pkendall64]

We have a branch for this which we can create a PR for once the CQL backend is merged.
https://github.com/orionhealth/janusgraph/tree/feature/vavr