book: fix typo issue into controller test
/*
-Ideally, we should have one `<kind>_conroller_test.go` for each controller scaffolded and called in the `suite_test.go`.
+Ideally, we should have one `<kind>_controller_test.go` for each controller scaffolded and called in the `suite_test.go`.
So, let's write our example test for the CronJob controller (`cronjob_controller_test.go.`)
*/
