Roll Observatory packages and add a roll script

packages/charted/lib/core/scales/log_scale.dart

 //
 // Copyright 2014 Google Inc. All rights reserved.
 //
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file or at
 // https://developers.google.com/open-source/licenses/bsd
 //
 part of charted.core.scales;
 
 /// Log scale is similar to linear scale, except there's a logarithmic
@@ skipping 160 matching lines @@
         return d / _pow((_log(d) + e).ceil()) <= k ? logFormatFunction(d) : '';
       } else {
         return d / _pow((_log(d) + e).floor()) <= k ? logFormatFunction(d) : '';
       }
     };
   }
 
   @override
   LogScale clone() => new LogScale._clone(this);
 }