Editorial: Add missing ISO spec number (#974)

Author: gibson042

spec/locales-currencies-tz.html

@@ -125,7 +125,7 @@ <h1>
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>It verifies that the _currency_ argument represents a well-formed 3-letter ISO currency code.</dd>
+        <dd>It verifies that the _currency_ argument represents a well-formed 3-letter ISO 4217 currency code.</dd>
       </dl>
       <emu-alg>
         1. If the length of _currency_ is not 3, return *false*.