Upgrade dependency to Jackson 2.10.x

[IRQs]

Dear contributors, I use your excellent Consul client in combination with quite a lot of other frameworks/clients (e.g. Dropwizard 2.0) that also depend on Jackson. All other clients have already migrated to Jackson 2.10.x (also using dependabot), resulting in compile time issues unless I explicitly exclude the Jackson dependencies from your Consul client.

There is already a pull request that would address this issue (#403), however, there seems to be a problem with your Continuous Integration (Travis). If you don't have the time, I can investigate it further, unless it was your intention to stay with Jackson 2.9.x for the time being.

[rickfast]

wasnt the intention, i just don't have a ton of time for this repo lately. pls feel free to investigate. thanks