Add new translation in Spanish (#670)

Added Spanish translations for "skip-to-content" link

src/partials/language/es.html

@@ -36,6 +36,7 @@
   "search.result.one": "1 documento encontrado",
   "search.result.other": "# documentos encontrados",
   "search.tokenizer": "[\s\-]+",
+  "skip.link.title": "Saltar a contenido",
   "source.link.title": "Ir al repositorio",
   "toc.title": "Tabla de contenidos"
 }[key] }}{% endmacro %}