tests: drop use of 'unittest2' (#1564)

diff --git a/tests/test_channel.py b/tests/test_channel.py
index 8a46bf0..fe33731 100644
--- a/tests/test_channel.py
+++ b/tests/test_channel.py
@@ -3,8 +3,8 @@
 
 __author__ = "jcgregorio@google.com (Joe Gregorio)"
 
-import unittest2 as unittest
 import datetime
+import unittest
 
 from googleapiclient import channel
 from googleapiclient import errors