[fix] typo in crossref settings: disable --> disabled

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings.yml

@@ -413,7 +413,7 @@ engines:
     engine: crossref
     shortcut: cr
     timeout: 30
-    disable: true
+    disabled: true
 
   - name: yep
     engine: json_engine