Watcher process leaks if using old version of HTTPoison

[chazsconi]

Due to edgurgel/httpoison#375 (which I created a PR to fix, and is now merged) if you use HTTPoison < v1.6.1 you will have a process leak when using watches whenever a GONE event is received from K8S.

Therefore should Kazan's deps be changed to force using this version or later of HTTPoison, or should this just be warned about in the docs?

I'm happy to create a PR for either option.

[obmarg]

Ah nice - I saw similar problems in a project I had based on HTTPoison a few years ago. Good to see someone fixing it.

I think it'd be fine to require > HTTPoison >= 1.6.1 - I'm assuming there's no breaking API changes, and people can always use an override: true dep if they really need an older verson.

[chazsconi]

OK - PR created. #74