mix docker.build producing error when building.

[haritimeset]

19:28:33.570 [error] Loading of /opt/app/_build/prod/lib/cowboy/ebin/cowboy_websocket_handler.beam failed: :badfile


19:28:33.570 [error] beam/beam_load.c(1287): Error loading module cowboy_websocket_handler:
  mandatory chunk of type 'Atom' not found



warning: behaviour :cowboy_websocket_handler is undefined
  lib/phoenix/endpoint/cowboy_websocket.ex:1

warning: function :cowboy_req.compact/1 is undefined (module :cowboy_req is not available)
  lib/phoenix/endpoint/cowboy_websocket.ex:73

warning: function :ranch.get_port/1 is undefined (module :ranch is not available)
  lib/phoenix/endpoint/cowboy_handler.ex:114

I am trying to deploy a phoenix app to production.
Elixir - 1.4.5 and Phoenix v1.2.4