utils/drifted_frq: Use python3 round builtin (W1633)

This changes the used rounding strategy.

See "Whats new in python3"[1] for more details:
> Exact halfway cases are now rounded to the nearest even result
> instead of away from zero.
> (For example, round(2.5) now returns 2 rather than 3.)

Fixes round-builtin (W1633) pylint error.

[1]: https://docs.python.org/3/whatsnew/3.0.html#builtins

Signed-off-by: Fabian P. Schmidt <kerel@mailbox.org>

.pylintrc

@@ -12,5 +12,3 @@ disable=
     R0914, # too-many-locals
     W0201, # attribute-defined-outside-init
     W0703, # broad-except
-# py3k transition issues:
-    W1633, # round-builtin

network/api/serializers.py

@@ -4,6 +4,7 @@ from __future__ import absolute_import, division
 
 from collections import defaultdict
 
+from future.builtins import round
 from rest_framework import serializers
 
 from network.base.db_api import DBConnectionError, get_transmitters_by_uuid_set

network/base/templatetags/tags.py

@@ -3,6 +3,7 @@ from __future__ import absolute_import, division
 
 from django import template
 from django.core.urlresolvers import reverse
+from future.builtins import round
 
 register = template.Library()