Fix a typo

Signed-off-by: Suguru Hirahara <did🔑z6MkvVZk1A3KBApWJXv2Ju4H14ErDfRGxh8zxdXSZ4vACDg5>

docs/configuring-playbook-dynamic-dns.md

@@ -42,7 +42,7 @@ ddclient_enabled: true
 
 ddclient_domain_configurations:
   - provider: example.net
-    protocol: dyndn2
+    protocol: dyndns2
     username: YOUR_USERNAME_HERE
     password: YOUR_PASSWORD_HERE
     domain: "{{ matrix_domain }}"