turn the ADDRESS country code into a MAY

We probably don't care too much as it's not meant to be parsed,
especially as there's no definitive format.
Anything that can be put on an envelope should be OK.

Author: robUx4

matroska_tags.xml

@@ -74,7 +74,7 @@ It **SHOULD** be a child of the following tags: "ARTIST", "LEAD_PERFORMER", or "
       <description lang="en">Email corresponding to the tag it's included in, using the "Addr-Spec" format defined in [@!RFC5322, section 3.4.1].</description>
     </tag>
     <tag name="ADDRESS" class="Nested Information" type="UTF-8">
-      <description lang="en">The physical address of the entity. The address **SHOULD** include a country code using the Country Code format defined in (#country-code-tags-formatting).
+      <description lang="en">The physical address of the entity. The address **MAY** include a country code using the Country Code format defined in (#country-code-tags-formatting).
 It can be useful for a recording label.</description>
     </tag>
     <tag name="FAX" class="Nested Information" type="UTF-8">