JATS template: fix equal-contrib attribute

The standard requires the value to be either `yes` or `no`, but is was
set to `true` for authors who contributed equally.

data/templates/article.jats_publishing

@@ -86,7 +86,7 @@ $endif$
 $if(author)$
 <contrib-group>
 $for(author)$
-<contrib contrib-type="author"$if(author.equal-contrib)$ equal-contrib="true"$endif$>
+<contrib contrib-type="author"$if(author.equal-contrib)$ equal-contrib="yes"$endif$>
 $if(author.orcid)$
 <contrib-id contrib-id-type="orcid">$author.orcid$</contrib-id>
 $endif$
@@ -208,4 +208,3 @@ $back$
 $endif$
 </back>
 </article>
-