update nats version and cleanup config

[rybit]

We were using an old library and the project has moved. I also cleaned up some of the config.

[smoya]

I am not in favor of having all configurations in the same package.
Instead, each package should know how to construct their own services from a config file (i.e.: nats.FromConfig(...).

By ensuring a clear separation of responsibilities and concerns we are:

• Allowing packages to just pick up their real dependencies and do not carry on code that is out of their domain.

I.e.: Service "Greeter" only needs a logger from nconf. By having nconf package as dependency, code related to Nats is gonna be pulled as well.

• Having a better code api as contexts are completely separated:

  logger, err := logs.FromConfig(...)
  natsClient, err := nats.FromConfig(...)

  VS

  logger, err := nconf.LoggerConfig{...}...
  natsClient, err := nconf.NatsConfig{...}...

• Avoiding nconf package code base growing unnecessary far from it's responsibility and instead use it across other packages (let me borrow the DDD terminology of "Shared Kernel" bounded context) here).

[rybit]

Ok after talking with @smoya we decided that we'd go with this scheme:

• config in the package is the default
• if you can't (import loops, etc) then we move the whole project to use the central config package.

The goal is to have a consistent approach across the project. Not some packages with their own config and some in the conf package

[smoya]

LGTM! 🚀