Merge pull request kubernetes-sigs#60 from justinsb/fix_slack_channel_typo

Fix typo: kubeuilder -> kubebuilder

Author: k8s-ci-robot

README.md

@@ -15,7 +15,7 @@ in sig apimachinery.
 
 You can reach the maintainers of this project at:
 
-- Slack channel: [#kubeuilder](http://slack.k8s.io/#kubebuilder)
+- Slack channel: [#kubebuilder](http://slack.k8s.io/#kubebuilder)
 - Google Group: [[email protected]](https://groups.google.com/forum/#!forum/kubebuilder)
 
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