fix: darkMode plugin

src/lib/darkMode.js

@@ -3,12 +3,10 @@ import { reactive } from 'vue';
 const darkModeMediaQuery = '(prefers-color-scheme: dark)';
 const matchMedia = window.matchMedia(darkModeMediaQuery);
 
-const darkMode = reactive({
-  value: matchMedia.matches,
-});
+const darkMode = reactive(matchMedia.matches);
 
 matchMedia.addEventListener('change', (event) => {
-  darkMode.value = event.matches;
+  darkMode = event.matches;
 });
 
 export const install = (app) => {