[mod] simple theme: drop img_src from default results

The use of img_src AND thumbnail in the default results makes no sense (only a
thumbnail is needed).  In the current state this is rather confusing, because
img_src is displayed like a thumbnail (small) and thumbnail is displayed like an
image (large).

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

searx/engines/apple_app_store.py

@@ -47,7 +47,7 @@ def response(resp):
                 'url': result['trackViewUrl'],
                 'title': result['trackName'],
                 'content': result['description'],
-                'img_src': result['artworkUrl100'],
+                'thumbnail': result['artworkUrl100'],
                 'publishedDate': parse(result['currentVersionReleaseDate']),
                 'author': result['sellerName'],
             }