This patch updates iso639_2_code value for Slovak language
Test plan:
1) Obtain a biblio record having 'slo' value in its language
code (marc field 041a)
2) Try to find it through Advanced search + more options
with language set to Slovak
3) Nothing is found
4) Apply this patch
5) Repeat steps 1 and 2
6) Record is found now
Signed-off-by: Mark Tompsett <mtompset@hotmail.com> Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl> Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>