Update argument type of reducer produced by combineReducers (#2115)
Update argument type of reducer produced by combineReducers (#2115)

* update argument type of reducer produced by combineReducers

* update Reducer type to use $Shape

* define CombinedReducer type

roth1002/redux,lifeiscontent/redux,CompuIves/redux,roth1002/redux,jas-chen/typed-redux,lifeiscontent/redux,jas-chen/redux,CompuIves/redux,gaearon/redux,gaearon/redux,jas-chen/redux,jas-chen/typed-redux