Fix typo in encrypt-data.md

Author: aaabramov

content/en/docs/tasks/administer-cluster/encrypt-data.md

@@ -368,7 +368,7 @@ To create a new Secret, perform the following steps:
        ...
        - name: enc                           # add this line
          mountPath: /etc/kubernetes/enc      # add this line
-         readonly: true                      # add this line
+         readOnly: true                      # add this line
        ...
      volumes:
      ...