fix type definition export

Author: timche

index.d.ts

@@ -4,7 +4,10 @@ type Action = {
 
 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 reduceReducers;
+export default function reduceReducers<S>(
+  initialState: S | null,
+  ...reducers: Reducer<S>[]
+): Reducer<S>;
+export default function reduceReducers<S>(
+  ...reducers: Reducer<S>[]
+): Reducer<S>;