Change syntax in Readme.md (redux-utilities#302)

* Fix syntax error in Readme.md

* Fix formatting

Author: cinan

README.md

@@ -46,12 +46,10 @@ const { increment, decrement } = createActions({
 
 const reducer = handleActions(
   {
-    [combineActions(increment, decrement)](
+    [combineActions(increment, decrement)]: (
       state,
-      {
-        payload: { amount }
-      }
-    ) {
+      { payload: { amount } }
+    ) => {
       return { ...state, counter: state.counter + amount };
     }
   },