error on deps.get

[gabrielmancini]

this dependencie https://github.com/emqx/emqtt/blob/master/rebar.config#L12 point to a fork of gun, and this fork has a dependency of a cowlib 2.8.0 but this emqtt it self needs 2.11.0

Dependencies have diverged:
* cowlib (Hex package)
  the dependency cowlib in deps/cowboy/rebar.config is overriding a child dependency:

  > In deps/cowboy/rebar.config:
    {:cowlib, "2.11.0", [env: :prod, hex: "cowlib", repo: "hexpm", optional: false]}

  > In deps/gun/rebar.config:
    {:cowlib, [env: :prod, override: true, git: "https://github.com/ninenines/cowlib", tag: "2.8.0"]}

  Ensure they match or specify one of the above in your deps and set "override: true"
** (Mix) Can't continue due to errors on dependencies

[amos-kibet]

#207