Bug 27881: Markup error in masthead-langmenu.inc

Bug 27881: Markup error in masthead-langmenu.inc

Some markup errors were introduced into the masthead-langmenu include
file by Bug 20168, presumably during the update to the dropdown menu
markup:

'<a class="dropdown-item" <a href="'

...resulting in validation errors like "Attribute <a not allowed on
element a at this point." This patch correct the errors.

To test you should have at least two languages enabled in the
OPACLanguages system preference, opaclanguagesdisplay set to "allow,"
and OpacLangSelectorMode set to "top" or "both top and footer."

- Apply the patch and view the OPAC.
- The "Languages" menu at the top of the page should look correct and
  work correctly.
- Validating the source of the page should return no errors related to
  the language menu's markup.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>