remove unintended change from default merge behaviour to identical bu…

…t manual one

targeted section of the README talks about integration with redux devtools. to accomplish this the dev needs to define third argument for `set` function. since arguments for `set` function are positional it means he/she needs to define the second, `replace`, argument as well

currently README suggests just to use `false` value for `replace` arg i.e. to override the default value by identical manual one, but defined on the dev side.

more clean way would be to use `undefined` at the second argument position that will make JS to use the default value, that is defined by lib authors, not dev

readme.md

@@ -401,7 +401,7 @@ const useBearStore = create(devtools((set) => ({
   ...
   eatFish: () => set(
     (prev) => ({ fishes: prev.fishes > 1 ? prev.fishes - 1 : 0 }),
-    false,
+    undefined,
     'bear/eatFish'
   ),
   ...
@@ -413,7 +413,7 @@ You can also log the action's type along with its payload:
   ...
   addFishes: (count) => set(
     (prev) => ({ fishes: prev.fishes + count }),
-    false,
+    undefined,
     { type: 'bear/addFishes', count, }
   ),
   ...