Update index.d.ts (#31)

Fix for #30 . Looks like the overloads for #29 were named correctly but the export was left incorrectly singular.

Author: tuuling

index.d.ts

@@ -7,4 +7,4 @@ type Reducer<S> = (state: S, action: Action) => S;
 function reduceReducers<S>(initialState: S | null, ...reducers: Reducer<S>[]): Reducer<S>;
 function reduceReducers<S>(...reducers: Reducer<S>[]): Reducer<S>;
 
-export default reduceReducer;
+export default reduceReducers;