[fix] version.py pep8 and py3 compatibility

searx/version.py

@@ -21,4 +21,6 @@ VERSION_MAJOR = 0
 VERSION_MINOR = 4
 VERSION_BUILD = 0
 
-VERSION_STRING = "%d.%d.%d" % (VERSION_MAJOR,VERSION_MINOR,VERSION_BUILD)
+VERSION_STRING = "{0}.{1}.{2}".format(VERSION_MAJOR,
+                                      VERSION_MINOR,
+                                      VERSION_BUILD)