[enh] py3 compatibility

searx/engines/duckduckgo.py

@@ -13,11 +13,11 @@
  @todo        rewrite to api
 """
 
-from urllib import urlencode
 from lxml.html import fromstring
 from requests import get
 from json import loads
 from searx.engines.xpath import extract_text
+from searx.url_utils import urlencode
 
 # engine dependent config
 categories = ['general']