Ensure transport module is loaded before checking exports

Tests were constantly failing without this patch. It seems ct
starts erlang code server in interactive mode, so application
module loading is defered.

src/ranch.erl

@@ -55,6 +55,7 @@
 start_listener(Ref, NbAcceptors, Transport, TransOpts, Protocol, ProtoOpts)
 		when is_integer(NbAcceptors) andalso is_atom(Transport)
 		andalso is_atom(Protocol) ->
+	_ = code:ensure_loaded(Transport),
 	case erlang:function_exported(Transport, name, 0) of
 		false ->
 			{error, badarg};