Compile gen_mod (2.1.13) gave error: gen_mod.erl:49: bad attribute

By following guide http://www.ejabberd.im/ejabberd-contrib, I checked out ejabberd modules and when tried to compile a module (any), it gave me error:

~/ejabberd-contrib/mod_admin_extra# ./build.sh
Recompile: ../ejabberd-dev/src/gen_mod
../ejabberd-dev/src/gen_mod.erl:49: bad attribute
../ejabberd-dev/src/gen_mod.erl:50: bad attribute

I don't know about Erlang, here is line 49-50 in gen_mod.erl:

-callback start(binary(), opts()) -> any().
-callback stop(binary()) -> any().

Please help, thank in adv.