docs: Fix title of DNS customization page (#985)

**What problem does this PR solve?**:

**Which issue(s) this PR fixes**:
Fixes #983 

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Author: jimmidyson

docs/content/customization/generic/dns.md

@@ -1,5 +1,5 @@
 +++
-title = "etcd"
+title = "DNS"
 +++
 
 This customization will be available when the