angular-dart: Update dart version range

examples/angular-dart/pubspec.yaml

 name: angular-dart-todomvc
 version: 0.0.0
 environment:
-  sdk: '>=1.0.0 <1.1.0'
+  sdk: '>=1.0.0 <=1.9.1'
 dependencies:
   angular: '>=0.9.0 <0.10.0'
   browser: '>=0.9.0 <0.10.0'