Update to rest-client ~> 2.0.2

[joshbenner]

Other sensu plugins (notably http) depend on a newer rest-client, which can make installation of the consul plugin in the same environment tricky.

I'm not sure what is required to update the consul plugin, but upon discussion in Slack, we agreed we should open a ticket to capture this as a concern.

[shayangz]

@majormoses any change of pushing this through? is causing issues as mentioned above. seems like there is already a PR in #65

[majormoses]

When I can find some time I can look into it but it looks to me like there are some breaking changes (which the tests caught) that need to be worked through: https://travis-ci.org/github/sensu-plugins/sensu-plugins-consul/jobs/673222570#L319

Anyone who wants to take a swing is more than welcome.