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/shooter.py b/y2017/control_loops/python/shooter.py
index a825ff0..69f0af4 100755
--- a/y2017/control_loops/python/shooter.py
+++ b/y2017/control_loops/python/shooter.py
@@ -285,7 +285,7 @@
             initial_t = 0
 
         last_U = numpy.matrix([[0.0]])
-        for i in xrange(iterations):
+        for i in range(iterations):
             X_hat = shooter.X
 
             if observer_shooter is not None: