[fix] unicode response in deezer and spotify

searx/engines/deezer.py

             if url.startswith('http://'):
                 url = 'https' + url[4:]
 
-            content = '{} - {} - {}'.format(
+            content = u'{} - {} - {}'.format(
                 result['artist']['name'],
                 result['album']['title'],
                 result['title'])

searx/engines/spotify.py

         if result['type'] == 'track':
             title = result['name']
             url = result['external_urls']['spotify']
-            content = '{} - {} - {}'.format(
+            content = u'{} - {} - {}'.format(
                 result['artists'][0]['name'],
                 result['album']['name'],
                 result['name'])