fix(typo): watch guide typo (#2989)

Update watchers.md

Author: ralacerda

src/guide/essentials/watchers.md

@@ -448,7 +448,7 @@ export default {
 
 Note that `onWatcherCleanup` is only supported in Vue 3.5+ and must be called during the synchronous execution of a `watchEffect` effect function or `watch` callback function: you cannot call it after an `await` statement in an async function.
 
-Alternaitvely, an `onCleanup` function is also passed to watcher callbacks as the 3rd argument<span class="composition-api">, and to the `watchEffect` effect function as the first argument</span>:
+Alternatively, an `onCleanup` function is also passed to watcher callbacks as the 3rd argument<span class="composition-api">, and to the `watchEffect` effect function as the first argument</span>:
 
 <div class="composition-api">