Merge pull request #779 from quantopian/pandas17

Change relativedelta to Timedelta as pandas 0.17.0 deprecated relativedelta.

zipline/data/us_equity_pricing.py

@@ -41,7 +41,6 @@ from pandas import (
     DataFrame,
     DatetimeIndex,
     read_csv,
-    to_datetime,
     Timestamp,
 )
 from six import (

zipline/utils/tradingcalendar.py

@@ -23,7 +23,7 @@ start = pd.Timestamp('1990-01-01', tz='UTC')
 end_base = pd.Timestamp('today', tz='UTC')
 # Give an aggressive buffer for logic that needs to use the next trading
 # day or minute.
-end = end_base + pd.datetools.relativedelta(years=1)
+end = end_base + pd.Timedelta(days=365)
 
 
 def canonicalize_datetime(dt):