docs: fixes url of link to Vue3 version

Author: luckylooke

docs/.vuepress/theme/Layout.vue

@@ -10,7 +10,7 @@
           <p>
             To read docs for Vue Test Utils for Vue 3,
             <a
-              href="https://next.vue-test-utils.vuejs.org/guide/"
+              href="https://test-utils.vuejs.org/"
               v-text="'click here'"
             />.
           </p>