fix(store): add type

src/store/index.ts

@@ -1,3 +1,4 @@
+import { Store } from 'redux';
 import configureStore from './configure-store';
 
 import { ReactFlowState, ConnectionMode } from '../types';
@@ -56,7 +57,7 @@ export const initialState: ReactFlowState = {
   reactFlowVersion: typeof __REACT_FLOW_VERSION__ !== 'undefined' ? __REACT_FLOW_VERSION__ : '-',
 };
 
-const store = configureStore(initialState);
+const store: Store = configureStore(initialState);
 
 export type ReactFlowDispatch = typeof store.dispatch;