Remove the pointless second argument to animate() in AnimatedValue.

sky/sdk/lib/widgets/toggleable.dart

Index: sky/sdk/lib/widgets/toggleable.dart
diff --git a/sky/sdk/lib/widgets/toggleable.dart b/sky/sdk/lib/widgets/toggleable.dart
index 9f36b8b1d057db6a5c65ca560e2e59de2302f70a..e6fac38ab4e640ba56dbab3b1ea257db022e9110 100644
--- a/sky/sdk/lib/widgets/toggleable.dart
+++ b/sky/sdk/lib/widgets/toggleable.dart
@@ -21,6 +21,7 @@ abstract class Toggleable extends AnimatedComponent {
     this.onChanged
   }) : super(key: key) {
     toggleAnimation = new AnimatedValue(value ? 1.0 : 0.0);
+    watch(toggleAnimation);
   }
 
   bool value;