[mod] engines - add askubuntu.com (Stack Exchange API)

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

searx/settings.yml

@@ -1130,6 +1130,12 @@ engines:
     api_site: 'stackoverflow'
     categories: it
 
+  - name: askubuntu
+    engine: stackexchange
+    shortcut: ubuntu
+    api_site: 'askubuntu'
+    categories: it
+
   - name: searchcode code
     engine: searchcode_code
     shortcut: scc