Upgrades flake8 from 1.5 -> 1.6

Also, removes flake8 ignores, since the warnings that were
at odds with eachother now work.

zipline/algorithm.py

@@ -24,9 +24,9 @@ from zipline.sources import DataFrameSource
 from zipline.utils.factory import create_trading_environment
 from zipline.transforms.utils import StatefulTransform
 from zipline.finance.slippage import (
-        VolumeShareSlippage,
-        FixedSlippage,
-        transact_partial
+    VolumeShareSlippage,
+    FixedSlippage,
+    transact_partial
 )
 from zipline.finance.commission import PerShare, PerTrade