Update cassowary dependency to 0.1.7

sky/sdk/example/rendering/simple_autolayout.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:sky';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/rendering/auto_layout.dart';
 import 'package:cassowary/cassowary.dart' as al;
@@ skipping 28 matching lines @@
 
     // The boxes must be stacked left to right
     p1.rightEdge <= p2.leftEdge,
     p2.rightEdge <= p3.leftEdge,
 
     // The widths of the first and the third boxes should be equal
     (p1.width == p3.width) as al.Constraint,
 
     // The width of the second box should be twice as much as that of the first
     // and third
-    (p2.width * al.CM(2.0) == p1.width) as al.Constraint,
+    (p2.width * al.cm(2.0) == p1.width) as al.Constraint,
 
     // The height of the three boxes should be equal to that of the container
     (p1.height == p2.height) as al.Constraint,
     (p2.height == p3.height) as al.Constraint,
     (p3.height == root.height) as al.Constraint,
 
     // The fourth box should be half as wide as the second and must be attached
     // to the right edge of the same (by its center)
-    (p4.width == p2.width / al.CM(2.0)) as al.Constraint,
-    (p4.height == al.CM(50.0)) as al.Constraint,
+    (p4.width == p2.width / al.cm(2.0)) as al.Constraint,
+    (p4.height == al.cm(50.0)) as al.Constraint,
     (p4.horizontalCenter == p2.rightEdge) as al.Constraint,
-    (p4.verticalCenter == p2.height / al.CM(2.0)) as al.Constraint,
+    (p4.verticalCenter == p2.height / al.cm(2.0)) as al.Constraint,
   ]);
 
   new SkyBinding(root: root);
 }