Roll Observatory packages and add a roll script

packages/quiver/lib/src/core/optional.dart

 // Copyright 2013 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 110 matching lines @@
    * Delegates to the underlying [value] operator==.
    */
   bool operator ==(o) => o is Optional && o._value == _value;
 
   String toString() {
     return _value == null
         ? 'Optional { absent }'
         : 'Optional { value: ${_value} }';
   }
 }