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/indexer.py b/y2017/control_loops/python/indexer.py
index 53b856c..0c5cb6b 100755
--- a/y2017/control_loops/python/indexer.py
+++ b/y2017/control_loops/python/indexer.py
@@ -215,7 +215,7 @@
     else:
       initial_t = 0
 
-    for i in xrange(iterations):
+    for i in range(iterations):
       X_hat = indexer.X
 
       if observer_indexer is not None: