Fixed unittest2 import error on Python 2.7

Changed all unittest2 imports to unittest

tests/finance/test_slippage.py

@@ -20,7 +20,7 @@ import datetime
 
 import pytz
 
-from unittest2 import TestCase
+from unittest import TestCase
 
 from zipline.finance.slippage import VolumeShareSlippage
 

tests/test_algorithm.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from unittest2 import TestCase
+from unittest import TestCase
 from datetime import timedelta
 import numpy as np
 

tests/test_exception_handling.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from unittest2 import TestCase
+from unittest import TestCase
 
 import zipline.utils.simfactory as simfactory
 from zipline.test_algorithms import (

tests/test_finance.py

@@ -18,7 +18,7 @@ Tests for the zipline.finance package
 """
 import pytz
 
-from unittest2 import TestCase
+from unittest import TestCase
 from datetime import datetime, timedelta
 
 from nose.tools import timed

tests/test_sorting.py

@@ -15,7 +15,7 @@
 
 import pytz
 
-from unittest2 import TestCase
+from unittest import TestCase
 from itertools import chain, izip_longest
 from datetime import datetime, timedelta
 from collections import deque

tests/test_sources.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from unittest2 import TestCase
+from unittest import TestCase
 
 import zipline.utils.factory as factory
 from zipline.sources import DataFrameSource

tests/test_transforms.py

@@ -18,7 +18,7 @@ import numpy as np
 import pandas as pd
 
 from datetime import timedelta, datetime
-from unittest2 import TestCase
+from unittest import TestCase
 
 from zipline import ndict
 

tests/test_utils.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from unittest2 import TestCase
+from unittest import TestCase
 from zipline.utils.factory import load_from_yahoo
 import pandas as pd
 import pytz