chore(examples): use cancelQueries in optimistic update example

Author: tannerlinsley

examples/optimistic-updates/pages/api/data.js

@@ -1,7 +1,7 @@
 const items = []
 
 export default async (req, res) => {
-  await new Promise(r => setTimeout(r, 500))
+  await new Promise(r => setTimeout(r, 1000))
 
   if (req.method === 'POST') {
     const { text } = req.body

examples/optimistic-updates/pages/index.js

@@ -17,6 +17,8 @@ export default () => {
       // the old value and return it so that it's accessible in case of
       // an error
       onMutate: text => {
+        queryCache.cancelQueries('todos')
+
         const previousValue = queryCache.getQueryData('todos')
 
         queryCache.setQueryData('todos', old => ({