Service tests fail to start child

[jparise]

I sometimes see these failures on Travis. When I do, it's for all service_test.exs tests. They may only occur under Elixir 1.7.

  1) test it handles returning a list (Thrift.Generator.ServiceTest)
     test/thrift/generator/service_test.exs:316
     ** (EXIT from #PID<0.1814.0>) shutdown: failed to start child: {:ranch_listener_sup, Thrift.Generator.ServiceTest.ServerSpy}
         ** (EXIT) an exception was raised:
             ** (MatchError) no match of right hand side value: false
                 (ranch) /home/travis/build/pinterest/elixir-thrift/deps/ranch/src/ranch_server.erl:98: :ranch_server.set_listener_sup/2
                 (ranch) /home/travis/build/pinterest/elixir-thrift/deps/ranch/src/ranch_listener_sup.erl:32: :ranch_listener_sup.init/1
                 (stdlib) supervisor.erl:295: :supervisor.init/1
                 (stdlib) gen_server.erl:374: :gen_server.init_it/2
                 (stdlib) gen_server.erl:342: :gen_server.init_it/6
                 (stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3