Fix some python2-isms in prep for python3

These ones should work in both versions so we don't have to do them as
part of a global change over.

Change-Id: I2177b329d385c50d706a50a750b6c115ea3ea7ae
diff --git a/y2017/control_loops/python/column.py b/y2017/control_loops/python/column.py
index 70cd649..7c34ee6 100755
--- a/y2017/control_loops/python/column.py
+++ b/y2017/control_loops/python/column.py
@@ -273,7 +273,7 @@
         profile.SetGoal(goal[2, 0])
 
         U_last = numpy.matrix(numpy.zeros((2, 1)))
-        for i in xrange(iterations):
+        for i in range(iterations):
             observer_column.Y = column.Y
             observer_column.CorrectObserver(U_last)