sumo_rest:options type is used but not defined

[lucafavatella]

Used e.g. in:
https://github.com/inaka/sumo_rest/blob/31b33efd327066c7fe1cfdbde624da87a2bc7120/README.md#sessions

sumo_rest/src/sr_state.erl

Line 24 in 31b33ef

#{ opts := sumo_rest:options()