HTML Plugin: update the new data directory name

Without this, the data files associated with the avocado_result_html
module won't be installed.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

optional_plugins/html/MANIFEST.in

-recursive-include avocado_result_html/resources *
+recursive-include avocado_result_html/templates *
 include VERSION
\ No newline at end of file