Fix bug in pkg:observe (observable_list.remove(Object))

pkg/observe/lib/src/observable_list.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of observe;
 
 /**
  * Represents an observable list of model values. If any items are added,
  * removed, or replaced, then observers that are listening to [changes]
  * will be notified.
@@ skipping 84 matching lines @@
     _list.addAll(iterable);
     int added = _list.length - len;
     if (hasObservers && added > 0) {
       _recordChange(new ListChangeRecord(len, addedCount: added));
     }
   }
 
   bool remove(Object element) {
     for (int i = 0; i < this.length; i++) {
       if (this[i] == element) {
-        removeRange(i, 1);
+        removeRange(i, i + 1);
         return true;
       }
     }
     return false;
   }
 
   void removeRange(int start, int end) {
     _rangeCheck(start, end);
     int length = end - start;
     _list.setRange(start, this.length - length, this, end);
@@ skipping 155 matching lines @@
       }
 
       offset += removed - added;
     }
   }
 }
 
 // TODO(jmesserly): bogus type to workaround spurious VM bug with generic base
 // class and mixins.
 abstract class _ListBaseWorkaround extends ListBase<dynamic> {}