Use Python native SkipTest

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/accounts/tests.py

@@ -25,7 +25,7 @@ Tests for user handling.
 import tempfile
 from unittest import TestCase as UnitTestCase
 from django.test import TestCase
-from django.utils.unittest import SkipTest
+from unittest import SkipTest
 from django.core.urlresolvers import reverse
 from django.contrib.auth.models import AnonymousUser, User, Group
 from django.core import mail

weblate/trans/tests/test_admin.py

@@ -20,7 +20,7 @@
 
 from weblate.trans.tests.test_views import ViewTestCase
 from django.core.urlresolvers import reverse
-from django.utils.unittest import SkipTest
+from unittest import SkipTest
 from weblate.trans.util import add_configuration_error
 from weblate import appsettings
 import tempfile

weblate/trans/tests/test_selenium.py

 from django.test import LiveServerTestCase
-from django.utils.unittest import SkipTest
+from unittest import SkipTest
 from selenium import webdriver
 from selenium.common.exceptions import WebDriverException
 from django.core.urlresolvers import reverse