Update Jedis client

[mknutty]

The current jedis client (2.9.0) came out in Dec 06, 2018. It conflicts with things like Spring Boot. It needs to be updated to a recent release.
Or better, switch to Lettuce like other projects.

[louis-launchdarkly]

Hello @mknutty, thank you for reaching out. From a quick read, Lettuce looks like a reasonable replacement for the existing Jedis client. At the very least, given Jedis client 6.0.0 just came out last week, we should move to a higher version.

I created SDK-1235 to track the work.