[fix] pep8

searx/utils.py

 ua_os = ('Windows NT 6.3; WOW64', 'X11; Linux x86_64; rv:26.0')
 ua = "Mozilla/5.0 ({os}) Gecko/20100101 Firefox/{version}"
 
+
 def gen_useragent():
     # TODO
     return ua.format(os=choice(ua_os), version=choice(ua_versions))