The tag is present in Lintian version 2.104.328. That is the most recent version we know about.
debian/watch file in this package doesn't start a
version= line. The first non-comment line of
debian/watch should be a
version= declaration. This
may mean that this is an old version one watch file that should be
updated to the current version.
Please refer to the uscan(1) manual page for details.