Return Reducer<S, AnyAction> from createReducer

This is more correct as the generated reducer does, in fact,
support passing actions other than the ones explicitly handled.
Also, this fixes an incompatibility with `configureStore` (#102).

src/createReducer.ts

@@ -46,14 +46,14 @@ export interface CaseReducersMapObject<S = any, A extends Action = AnyAction> {
 export function createReducer<S = any, A extends Action = AnyAction>(
   initialState: S,
   actionsMap: CaseReducersMapObject<S, A>
-): Reducer<S, A> {
+): Reducer<S> {
   return function(state = initialState, action): S {
     // @ts-ignore createNextState() produces an Immutable<Draft<S>> rather
     // than an Immutable<S>, and TypeScript cannot find out how to reconcile
     // these two types.
     return createNextState(state, (draft: Draft<S>) => {
       const caseReducer = actionsMap[action.type]
-      return caseReducer ? caseReducer(draft, action) : undefined
+      return caseReducer ? caseReducer(draft, action as A) : undefined
     })
   }
 }

type-tests/files/createReducer.typetest.ts

@@ -16,13 +16,10 @@ import { AnyAction, createReducer, Reducer } from 'redux-starter-kit'
     decrement: decrementHandler
   })
 
-  const numberReducer: Reducer<number, CounterAction> = reducer
+  const numberReducer: Reducer<number> = reducer
 
   // typings:expect-error
-  const stringReducer: Reducer<string, CounterAction> = reducer
-
-  // typings:expect-error
-  const anyActionReducer: Reducer<number, AnyAction> = reducer
+  const stringReducer: Reducer<string> = reducer
 }
 
 /**