CC-BY-ND-4.0: Include CC0 dedication

This is in upstream's current text [1], and seems to have been added
between [2] and [3].  Use the <optional> wrapper so we continue to
match both the old and new versions.

[1]: https://creativecommons.org/licenses/by-nd/4.0/legalcode
[2]: https://web.archive.org/web/20141111232312/https://creativecommons.org/licenses/by-nd/4.0/legalcode
[3]: https://web.archive.org/web/20141119001617/https://creativecommons.org/licenses/by-nd/4.0/legalcode

Author: wking

src/CC-BY-ND-4.0.xml

@@ -420,13 +420,15 @@
         </list>
       <p>Creative Commons is not a party to its public licenses. Notwithstanding, Creative Commons may elect to
          apply one of its public licenses to material it publishes and in those instances will be considered
-         the “Licensor.” Except for the limited purpose of indicating that material is shared under a Creative
-         Commons public license or as otherwise permitted by the Creative Commons policies published at
-         creativecommons.org/policies, Creative Commons does not authorize the use of the trademark “Creative
-         Commons” or any other trademark or logo of Creative Commons without its prior written consent
-         including, without limitation, in connection with any unauthorized modifications to any of its public
-         licenses or any other arrangements, understandings, or agreements concerning use of licensed material.
-         For the avoidance of doubt, this paragraph does not form part of the public licenses. 
+         the “Licensor.” <optional>The text of the Creative Commons public licenses is dedicated to the public
+         domain under the CC0 Public Domain Dedication.</optional> Except for the limited purpose of indicating
+         that material is shared under a Creative Commons public license or as otherwise permitted by the
+         Creative Commons policies published at creativecommons.org/policies, Creative Commons does not
+         authorize the use of the trademark “Creative Commons” or any other trademark or logo of Creative
+         Commons without its prior written consent including, without limitation, in connection with any
+         unauthorized modifications to any of its public licenses or any other arrangements, understandings, or
+         agreements concerning use of licensed material. For the avoidance of doubt, this paragraph does not
+         form part of the public licenses.
         <br/>Creative Commons may be contacted at creativecommons.org. </p>
     </license>
-</SPDXLicenseCollection>
+</SPDXLicenseCollection>