docs: fix pull request url for getters note (#2018)

Co-authored-by: Kia King Ishii <[email protected]>

Author: jrnewton

docs/guide/getters.md

@@ -17,7 +17,7 @@ If more than one component needs to make use of this, we have to either duplicat
 Vuex allows us to define "getters" in the store. You can think of them as computed properties for stores.
 
 ::: warning WARNING
-As of Vue 3.0, the getter's result is **not cached** as the computed property does. This is a known issue that requires Vue 3.2 to be released. You can learn more at [PR #1883](https://github.com/vuejs/vuex/pull/1883).
+As of Vue 3.0, the getter's result is **not cached** as the computed property does. This is a known issue that requires Vue 3.1 to be released. You can learn more at [PR #1878](https://github.com/vuejs/vuex/pull/1878).
 :::
 
 Getters will receive the state as their 1st argument: