Use correct field when reading WipScope

Closes https://github.com/google/webkit_inspection_protocol.dart/issues/49
diff --git a/lib/src/debugger.dart b/lib/src/debugger.dart
index 5c3808b..fa4c428 100644
--- a/lib/src/debugger.dart
+++ b/lib/src/debugger.dart
@@ -160,7 +160,7 @@
   WipScope(this._map);
 
   // "catch", "closure", "global", "local", "with"
-  String get scope => _map['scope'] as String;
+  String get scope => _map['type'] as String;
 
   /// Object representing the scope. For global and with scopes it represents
   /// the actual object; for the rest of the scopes, it is artificial transient